OSHA released its long awaited emergency temporary standard (ETS) last week that calls for employers with 100 or more employees to either implement a vaccine mandate or ensure workers are undergoing weekly COVID-19 testing and wearing face masks at work. The rule covers temporary workers, seasonal workers, and minors.

“COVID-19 has had a devastating impact on workers, and we continue to see dangerous levels of cases. We must take action to implement this emergency temporary standard to contain the virus and protect people in the workplace against the grave danger of COVID-19,” U.S. Labor Secretary Marty Walsh said in a statement. 

Yet not even 24 hours after the regulation was released, companies and organizations filed lawsuits in several federal circuit courts, including the Fifth, Sixth, Eighth, and Eleventh, seeking to stop the ETS from going into effect. On Saturday, the Fifth Circuit, which oversees Louisiana, Mississippi, and Texas, issued an order granting the temporary stay. Most likely, all of the lawsuits will be combined and then a single federal court (likely the U.S. Supreme Court) will hear the case. 

The temporary reprieve does raise questions for employers. The Fifth Circuit’s ruling is particularly nebulous because the court did not specifically state whether the stay applied only in the Fifth Circuit or nationwide, says James Seegers, a partner with BakerHostetler focused on employment and labor law. 

“The Fifth Circuit stay confuses the landscape, just as employers were starting to put their compliance approaches together,” says Timothy J. Bartl, president and CEO of the HR Policy Association. The organization represents HR officers from more than 390 of the largest U.S. employers.

But that shouldn’t stop employers from moving forward with their planned compliance, Bartl tells Fortune. “Because we’re not certain about the path that the legal challenges are going to take, employers need to assume that the ETS is going to take effect as planned and be prepared to adjust accordingly, as developments happen,” he notes. 

“In the event that the ETS is allowed to go into effect, employers need to be ready,” Bartl says. Although some legal challenges to COVID-related restrictions have prevailed, Bartl says it’s unclear on how courts will rule on this specific OSHA regulation. “Employers need to be nimble, and they need to prepare as if they’ve got to comply.”

That’s particularly critical given that OSHA’s new rules require unvaccinated workers to wear face masks at work beginning Dec. 5, as well as force companies to put policies in place that offer paid leave to receive and recover from the COVID-19 vaccine. According to OSHA’s rules, employees need to be fully vaccinated or begin weekly testing by Jan. 4, 2022. It’s worth noting that the Moderna and Pfizer vaccines require a respective 28-day and 21-day waiting period in between doses followed by another two-week period after the last shot before an employee reaches “fully vaccinated” status.

“Those deadlines require that employers start taking action now in order to ensure full compliance and avoid serious penalties,” Seegers says. 

Robert Lian, a lawyer focusing on labor and employment litigation at Akin Gump in Washington, D.C., agrees. “The time frames for compliance under the ETS are very tight,” he tells Fortune. Until a court enjoins the rule after hearing from the parties on the merits—not just a temporary stay like the Fifth Circuit issued on Saturday—employers should assume that the ETS remains the law of the land and that the dates and deadlines remain in effect.

And while Lian says the Fifth Circuit is operating on an “extraordinarily fast schedule” (the court ordered the Biden administration to respond by Monday at 5 p.m., for example), the case will likely move beyond just the circuit courts.

Ultimately the Supreme Court is probably going to have to decide this, and that’s probably not going to happen before Dec. 5, when the first set of requirements kick in, says Jim Brudney, a professor of labor and employment law at Fordham Law School.

Even with the legal uncertainty, Brudney says he expects there will be a “fair amount of activity” among companies working to comply with the new regulation. “For those employers who had no interest in doing this or feel pressured not to do it by other circumstances, they may wait. But the detail and nuance of the regulation creates a set of…sequenced steps that employers can take, and I would expect that many of them will take those steps, even as the litigation is winding its way to the Supreme Court,” Brudney notes. 

That’s because there are real public health and economic risks at play. “The more immediate risk is that if you don’t do the things that OSHA has concluded are necessary to address this emergency, do you risk some serious potential problems with your workforce?” Brudney says.

Companies that fail to comply may also face enforcement actions and fines. Under the ETS, OSHA can fine qualifying employers up to $13,653 for each violation of the regulation and up to $136,532 for repeat offenses. If the Build Back Better Act is enacted, the maximum fine would increase to $700,000.

“There are a number of steps that are necessary to ensure the Dec. 5 and Jan. 4 vaccination dates are met. Waiting may seriously limit the options available to employers,” Lian adds. 

Both Brudney and Bartl say that OSHA’s goal here is to preserve safety and health in the workplace; the agency is not rolling out this ETS to be punitive. However, Bartl isn’t ruling out that OSHA will perform some targeted initiatives to demonstrate its seriousness. 

“The most significant risk of waiting to move forward with OSHA’s ETS is that the stay will be lifted and ultimately the standard allowed to go into effect, with those covered employers that delayed having lost time to at least begin taking steps to prepare for ETS’s effective date,” says Gregory Abrams, a lawyer with Faegre Drinker Biddle & Reath.

“The government has made clear it believes OSHA’s ETS is constitutional and may not indulge any delay in compliance due to a ‘wait and see’ approach,” Abrams adds.