New York ? Here’s what it could look like: Bicyclists darting through never-ending traffic jams. Swarms of commuters trudging over the Brooklyn Bridge in their sneakers in the freezing cold. Tourists stranded during the height of the Christmas season. Broadway shows with half-empty theaters.

New York could be hit on Friday with its first subway and bus strike in more than 25 years, a walkout that could shut down a system used by an estimated 7 million riders a day.

The Metropolitan Transportation Authority is locked in round-the-clock negotiations with the Transport Workers Union on a new contract for more than 33,000 members. The old contract expires at 12:01 a.m. Friday.

Estimates are that it would cost the city hundreds of millions per day in overtime and lost business and productivity.

A strike could be costly for the union, too. A walkout would be illegal under state law, and workers could face tough penalties. Strengthening the MTA’s hand, a judge issued an injunction Tuesday that bars the workers from striking.

They could lose two days’ pay for every day on strike. And the city is asking for additional damages against individual transit workers: $25,000 for the first day of the walkout, doubling each day thereafter.