One in four companies has instituted a vaccine mandate for U.S. workers, a sharp increase from last month, following President Joe Biden’s directive ordering large employers to require shots or weekly testing.

Another 13% of companies plan to put a mandate in place, according to Brian Kropp, chief of human-resources research at consultant Gartner. The firm’s findings are based off a survey of roughly 400 organizations.

Last month, just 16% of companies had vaccine mandates, Gartner data show, but Biden’s Sept. 9 directive has sent employers scrambling to come up with plans to adhere to the new rules. About 20% of the most recent survey’s respondents haven’t decided what to do yet, Kropp said, indicating that the remaining companies — about 40% — might ultimately decide to test their employees instead of enforcing inoculations.

Companies expect to lose between 2% and 8% of their employees due to vaccine mandates, Gartner found, either because they quit or they’re terminated for noncompliance.

“If you’re at 2%, you can live with that,” Kropp said in a panel discussion Thursday. “If it’s 8%, that could be a real problem, especially if it’s concentrated in one place or in one department.”

The details of Biden’s emergency regulation, which will come from the Department of Labor’s Occupational Safety and Health Administration and applies to private employers with 100 or more workers, haven’t been developed yet. But companies “don’t have the luxury of waiting for the feds to write the rules,” Kropp said in the panel, sponsored by Protocol, a technology news site.

Either choice presents pitfalls for managers. A vaccine mandate could result in staff defections and hurt a corporate culture, while testing raises thorny questions about how to administer, record and pay for all the swabbing.

“Testing people weekly is a heavy lift,” Rachel Conn, an employment lawyer and partner at law firm Nixon Peabody, said on the panel. “Just having a mandate could be easier potentially.”

Another problem, Kropp said, is that while companies expect the OSHA regulation to come in force by the end of the year, some employees believe it could get overturned in the courts. The attorney general of Arizona filed a lawsuit earlier this month to stop the vaccine requirement, the first legal salvo against it, and others will likely follow once the details are promulgated.

“The bigger problem employers have is there are employees who believe the Supreme Court will overturn it,” Kropp said. “A lot of employees who haven’t gotten the shot yet don’t believe this is real. So there’s the legal part of it, and the perception part, and you have to manage both of those things.”

The federal vaccine directive, officially known as an emergency temporary standard, or ETS, doesn’t state whether fully remote workers will have to get their shots as well. California, one of 22 states that has its own OSHA rules, has said that employees working from home don’t fall under its mandate. But the new COVID vaccine rules for federal contractors does include remote workers, so it’s unclear how OSHA will treat them.