As the delta variant of the coronavirus has derailed the anticipated post-Labor Day return to in-person work, some employers are turning to vaccine mandates to get their workers back in the office.

About 52% of employers anticipate instituting a vaccine mandate by the end of the year, according to a survey from consulting firm Willis Towers Watson of nearly 1,000 companies that collectively employ 10 million people, Bloomberg and The New York Times report. About 21% of survey respondents have already instituted mandates.

The full Food and Drug Administration approval granted to the Pfizer-BioNTech vaccine gave employers firmer ground to require vaccines, though the Occupational Safety and Health Administration has clarified that employers who do require a vaccine would be potentially liable in the case of side effects. The Moderna vaccine has been officially submitted for full FDA approval, which generally takes months but was completed in 97 days for Pfizer, CNN reports.

An additional strategy companies take could be increasing health insurance premiums for the unvaccinated. Fourteen percent of respondents in the Willis Towers Watson survey said they are considering doing so, while between 1% and 2% already have instituted surcharges for the unvaccinated.

“Companies have been doing a really good job of making it easy to be vaccinated,” Willis Towers Watson Health Management Practice Population Health Leader Dr. Jeff Levin-Scherz told Bloomberg. “Employers are now thinking, ‘How can we make it difficult for people not to be vaccinated?’”

Being vaccinated has become a condition of employment for new hires in an increasing number of job postings, with job search website Indeed showing a 90% increase in vaccine requirements in its listings between July and August. Major real estate companies Related Cos. and The Durst Organization vowed in August to fire employees who refused a vaccine. Coworking operator Convene instituted a vaccine requirement not just for its own employees but for all members and their guests as a condition of entrance.

Though it constitutes the majority of companies in the Willis Towers Watson survey, a 52% share of employers planning to mandate vaccination represents a sharp decrease from the 90% of employers who were considering a vaccine mandate in March when the rollout of the vaccine began expanding to all adults.

For employers who wanted in-person work to resume after the Labor Day holiday weekend, the delta variant not only increased the short-term risk but caused some employees to dig in further on their demands for long-term incorporation of remote work. A vaccine requirement may be used as a counterpoint or a demonstration of office users' commitment to safety.