As coronavirus cases rise again in cities throughout the United States and fear over the omicron variant grows, more companies are requiring or planning to mandate vaccines for their employees.

A new report from consulting firm Willis Towers Watson has found that 57% of U.S. employers now require or are planning to mandate vaccines for their workers in the coming months. Thirty-two percent of those employers, however, said they will require vaccinations only if the federal vaccine mandate takes effect.

The Biden administration's vaccine mandate for private businesses has been put on hold as a federal appeals court reviews the rules, but many companies including Google, Microsoft and Ford have already implemented their own vaccine requirements.

Still, some companies have been hesitant to require their workers to get the shot for fear of losing talent in a tight labor market. "Some workers have said they won't come back to the office unless people are vaccinated and other folks have said they would leave their companies if they required them to be vaccinated," Elise Freedman, a workforce transformation practice leader at Korn Ferry who is helping companies coordinate their return-to-office plans, tells CNBC Make It.

The companies that do have vaccine mandates are at risk of making "big mistakes" that could drive workers away, she warns. Below, Freedman shares the two mistakes she's noticed companies make when enacting their vaccine policies, and what leaders should do instead.

1. Not setting clear rules or expectations

The second step an organization should take after announcing vaccine requirements is to tell employees how the decision was made — otherwise, it could be difficult for them to understand the new rules and trust company leadership, Freedman notes.

"The advice I keep repeating to my clients is communicate, communicate, communicate," she adds. "Tell people why these new policies are in place: Is it because of your customer base, the type or work you're doing, or a different reason?"

Managers should also provide reliable, accurate information about the vaccines from sources such as The World Health Organization (WHO) or The Centers for Disease Control and Prevention (CDC), Freedman says, and encourage workers to ask questions.

There should also be open communication about new virus variants, travel restrictions and other major announcements related to the pandemic. "Companies should send a note to their employees noting that they're continuing to monitor the situation and appreciate their support as more information becomes available," Freedman suggests.

2. Not helping employees get vaccinated or tested

Some employers will ask employees to get the shot or tested before coming into the office with no guidance or resources on how to do so. "Companies are still struggling with how to pay for coronavirus tests, if they will absorb the cost or ask unvaccinated employees to pay," she says. "Sometimes you have to have hard, awkward conversations with candidates or employees."

Freedman recommends companies do "whatever they can" to make it as convenient as possible for people to get vaccinated whether it is giving employees time off to do it, setting up an on-site vaccination center at their office or teaming up with local pharmacies to schedule appointments for employees.

The same logic applies to testing, for unvaccinated employees: companies should consider an on-site testing center, help employees find testing sites and make it clear whether an employee is responsible for the cost of testing or not.

"People's anxiety is still high — we have the holidays coming up, and now this new variant has come out," Freedman says of the challenges ahead. "But the most important step companies can take right now to navigate this uncertain time is coming up with their long-term pandemic plan and telling employees how they can prepare."

Check out:

New York City will now require private workers to get vaccinated—and other cities could follow

How the omicron variant could impact return-to-office plans: 'We're dealing with rapidly moving facts'

'The most guilt-ridden, nightmare time of year': how to avoid holiday season burnout at work

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