New York ? New York City transit workers voted Saturday to authorize a strike that could shut down bus and subway service at the height of the holiday shopping season.

Thousands of members of Transport Workers Local 100 voted unanimously to authorize their leaders to call a walkout if the union and the Metropolitan Transportation Authority can’t agree on a new contract by midnight Thursday, when the current contract expires.

MTA officials said they were optimistic an agreement would be reached. State law prohibits strikes by public employees, and union workers would face huge fines if they walked off the job.

The system shuttles more than 7 million riders throughout the city on an average day.

The MTA last week offered a proposal that would give workers a 3 percent raise in the first year and a conditional raise of 2 percent the second year. The union rejected the offer, which also proposed changes to workers’ retirement and health benefits.