Workers at businesses with more than 100 employees must be vaccinated for COVID-19 or undergo weekly testing starting Jan. 4, under a new federal rule released Thursday.

The new details immediately prompted an outcry from Republican leaders in Iowa who oppose COVID-19 vaccine mandates, and Gov. Kim Reynolds vowed to sue over the requirement. 

Once in effect, the new rule could cover more than 923,000 Iowa employees who work for 2,200 businesses. 

In Iowa, employers must now navigate the new regulations, as well as a brand-new state law that the Iowa Legislature passed last week in anticipation of the federal rule. The law attempted to soften some of the effects of the rule by requiring employers to accept religious and medical exemptions for the COVID-19 vaccine while also extending unemployment benefits to those fired for not complying with vaccine mandates. 

Here's what you need to know about the new rule, Iowa's new law, and what happens next. 

The new federal rule will apply to workers at businesses with 100 or more employees. Employers could be slapped with penalties of up to $13,600 per violation if they don’t comply.

The rule doesn't apply to people who work from home, but it would require testing for unvaccinated hybrid workers if they're reporting to the office during a given week. 

In Iowa, the rule also appears to apply to state and local government employers with 100 or more employees, including teachers and school staff. That's because Iowa is among 21 states that have the option of writing their own workplace rules for public and private sector workers. But those rules can’t be weaker than what the federal government is requiring – and must be adopted in 30 days.

A spokesperson for Reynolds did not comment Thursday on whether the state plans to follow the requirements for state employees. 

Workers are considered fully vaccinated if they have taken two doses of either the Moderna or Pfizer-BioNTech vaccines, or one dose of the Johnson & Johnson, by Jan. 4. Employers must give employees paid time off to get vaccinated and recover from side effects. 

More:Iowa will get more than 99,000 COVID vaccines for kids 5-11 this week

Currently, 68% of Iowans 18 and older are fully vaccinated for COVID-19, according to Centers for Disease Control and Prevention data. But there has been significant resistance among the remaining Iowans who are unvaccinated. A September Des Moines Register/Mediacom Iowa Poll found one in four Iowa adults does not plan to take the vaccine. 

The rule allows workers to undergo weekly testing as an alternative, although they may have to bear the cost of the testing themselves.

The rule would also require unvaccinated employees wear a face mask on the job beginning Dec. 5.

Businesses can be tougher than the rules require and can mandate workers get vaccinated, rather than giving them the option of regular testing.

More:Gov. Kim Reynolds says she 'will take immediate legal action' on Biden's vaccine mandate

Simply put: Yes and yes. 

But the details of how the federal exemption process will interact with a new Iowa law that involves religious exemptions remain somewhat murky.

Religious and medical exemptions for employee vaccination requirements have already been allowed under federal law. Federal guidance says employers must make "reasonable accommodations" for employees who refuse the vaccination due to disability, religious belief or pregnancy. Those accommodations could include a testing alternative under the new rule. 

In anticipation of the new federal rule, Reynolds signed a new law last week that attempts to grant Iowans wider latitude to claim medical and religious exemptions from employer COVID-19 vaccination mandates. It appears to go further than federal law by giving employers less of an option to turn down an employee's claim for an exemption if there's not a reasonable accommodation available — or if they suspect it's not a legitimate medical reason or religious belief.

The law says employers "shall" waive a vaccine requirement for an employee who submits a statement that receiving the vaccine would be "injurious" to their health or well-being, or that it conflicts "with the tenets and practices" of a religion the employee adheres to or belongs to. The statement would not need to be attested by a physician or a faith leader.

Public health experts say the shots are safe and very effective at preventing severe illness from COVID-19.

The new law also specifies that employees must request a waiver and submit a statement but does not specify a specific form employees must use. Iowans seeking an exemption can check with their employer about how to make the request.

More:Gov. Kim Reynolds signs law expanding exemptions from employer vaccine mandates; joins lawsuit against Biden

The new law has already affected some hospitals that put their own vaccine mandates in place. MercyOne delayed its Nov. 1 deadline until Nov. 12 as hospital leaders work through the new law's implications. UnityPoint planned to place employees who hadn't complied by Nov. 1 on leave while leaders sort out who qualifies for exemptions. 

State leaders said Thursday they were still examining the rule and did not offer clarification on how Iowa's new state law could affect enforcement of the federal rule when it comes to who qualifies for an exemption. Several Iowa businesses also said they were still looking through the new rule. 

Whether Iowa's expanded exemptions will allow more employees to circumvent Biden's vaccine requirements remains unclear, said Denise Hill, an associate professor at Drake University who has written a book on vaccine mandates and also practices as an attorney and mediator with the Whitfield & Eddy law firm. 

"I think that this is sort of a novel approach that Iowa has taken, and if it's found to be successful, I definitely can see other states that have similar objectives following suit," Hill said.

Senate Minority Leader Zach Wahls, D-Coralville, said Thursday there is still confusion on how Iowa's new law will intersect with the federal requirements, and it may require legal action to sort through. 

“I do think that there’s substantial concern on how those two laws are going to intersect — on the exemption piece in particular — and so I think that’s, unfortunately, a question that will likely have to be answered by the courts because I don’t know if there’s a lot more that the state legislative branch can do," he said. 

In addition to expanding exemptions, Iowa's new law also allows Iowans fired for not complying with vaccine mandates to qualify for unemployment benefits.

Though the law gained support from most Republicans and several Democrats, it faced pushback from businesses, who said the new law could place employers in a difficult position, as well as from groups that oppose vaccine mandates, who didn't believe the law went far enough to ban mandates. 

More:Most Des Moines hospital staff comply with vaccine mandates by getting shots or exemptions

The Iowa Department of Public Health has a search tool to assist Iowans with finding a vaccine provider in their area. 

That is available at vaccinate.iowa.gov/providers.

COVID-19 tests are now widely available from a variety of sources and in a variety of forms. The statewide Test Iowa program offers free, take-home test kits where Iowans collect their own saliva and mail it to the state lab at the University of Iowa for analysis.

The state health department recently added drop-off sites in large cities around the state where Iowans can submit their tests for same-day delivery to the state lab. 

Iowa’s coronavirus testing system includes several options ranging from local clinics and pharmacies — like Hy-Vee, Walgreens and CVS — to private firms like GS Labs in West Des Moines, which charges $380 per test out of pocket to those who don’t have insurance. 

Providers offer different types of tests, including PCR tests, rapid antigen tests and antibody tests. 

The state last month launched a testing locator map to help connect Iowans with tests in their area. The map is available on the state's coronavirus website. 

►More: Where can you find a COVID test? From rapid tests to free take-home tests, here's where to get one in Iowa

Iowa Republican leaders immediately pushed back against the new rule Thursday, saying they don't believe in COVID-19 vaccination mandates. 

Reynolds vowed to take legal action against the mandate. Last week, Reynolds had also joined nine other states in suing the Biden administration over its vaccination requirement for federal workers. The new lawsuit will be separate. 

“Biden’s plan pits Americans against Americans while forcing them to choose between making a living or standing up for their personal beliefs," said Reynolds, who is vaccinated for COVID-19 but has been a staunch opponent of mandating the shots. "Biden’s actions will only worsen the existing workforce shortages and supply chain issues that hinder our economic recovery."  

Republican Party of Iowa chair Jeff Kaufmann said in a statement that the party supports Reynolds' lawsuit and that the Biden administration "has has absolutely overstepped their power." 

Democrats responded by praising Biden's leadership on the pandemic. Wahls said Republicans haven't presented a plan to end the pandemic. 

"At least the Biden administration is doing something," he told reporters Thursday. "What are the Republicans doing?"

Regarding confusion surrounding Iowa's new law, iowa Democratic Party chair Ross Wilburn said that speed has likely led to uncertainty around how it will work. 

"The confusion is understandable given the pace that this was put together," Wilburn said.  

USA Today contributed to this report.

Ian Richardson covers the Iowa Statehouse for the Des Moines Register. Reach him at irichardson@registermedia.com, at 515-284-8254, or on Twitter at @DMRIanR.