Outgoing New York City Mayor Bill de Blasio announced a wide-ranging vaccine mandate for the city’s private employers, a move expected to impact roughly 184,000 businesses, including many commercial real estate firms, and draw immediate legal challenges.

Announced Monday and set to take effect Dec. 27, the step is a first-in-the-nation move by a municipality. President Joe Biden’s mandate, currently the subject of legal challenges, only applied to firms with more than 100 employees.

“New York City will not give a single inch in the fight against Covid-19,” de Blasio, who will leave office less than a week after the mandate is set to go into effect, said in a statement. “Vaccination is the way out of this pandemic.”

The mayor's office plans to offer additional guidance and announce a small-business support initiative on Dec. 15. Mayor-elect Eric Adams, also a Democrat, will take office on Jan. 1 and has declined to commit to upholding the vaccine mandate for private employers.

SquareFoot CEO Michael Colacino told The Wall Street Journal that his real estate firm had gotten into a good rhythm working in the office with masking for unvaccinated workers, and this announcement felt ”a little bit out of the blue.”

Bisnow asked leading CRE and construction firms in early November about their vaccination programs, and the vast majority declined to respond. There’s worry within the construction industry, which has significantly lower vaccination rates than other industries, that a vaccine mandate would make it even more difficult to retain and find workers.

Challenges to the city’s mandate are expected, and by bringing a case to a different federal circuit than those currently evaluating the federal mandate, may create a split among circuits and accelerate a hearing on the issue in front of the U.S. Supreme Court.