New York City employees are now required to get vaccinated. And so are state workers in California.

But in Philadelphia, Mayor Jim Kenney’s administration isn’t requiring vaccines for city workers.

Officials “strongly encourage” city employees to get shots to protect against COVID-19 and are offering four hours of comp time for workers who provide a copy of their vaccination cards, said Joy Huertas, a city spokesperson. And the administration hasn’t ruled out the possibility of requiring vaccination in the future.

“We will continue to assess the need to implement a vaccination mandate for our city workers and may make this a requirement at a future date,” Huertas said Tuesday.

New York City and California announced their new requirements Monday, amid concern that the delta variant of the coronavirus and its rapid spread are increasing case counts and posing a serious threat to unvaccinated Americans. San Francisco officials announced in June that it would require all city workers to be vaccinated. And the U.S. Department of Veterans Affairs also announced Monday that its health-care workers must get vaccinated in the next eight weeks.

» READ MORE: University of Pennsylvania Health System makes rare move to require COVID-19 vaccines for employees

The University of Pennsylvania Health System, with 44,000 employees, and other health-care providers are requiring vaccination for their workers. And a coalition of medical professional groups called on Monday for mandatory vaccination for all U.S. health-care workers.

Philadelphia City Hall and other city buildings reopened to the public this month, and employees who had been working remotely began gradually returning to offices. Huertas said the city health department’s new guidance recommending that masks be worn indoors did not affect that plan or timeline.

Masks are required in city buildings for unvaccinated workers and visitors and strongly recommended for everyone, Huertas said.

The federal Centers for Disease Control and Prevention updated its mask guidance Tuesday, recommending that masks be worn indoors by both vaccinated and unvaccinated people in areas of the country where the coronavirus is surging.