Three large unions in greater Philadelphia are all threatening to strike at the same time in a move that could "shut the region down," according to one union boss.

Thousands of Philadelphia city workers are preparing to walk off the job, if a new contract isn't reached. More than 9,000 employees, who work in prisons, sanitation and 911 dispatch, realize a strike would create a major impact.

PHILADELPHIA (WPVI) -- Philadelphia's largest city workers union has voted to authorize a strike. The results announced Thursday showed 87% of workers voted in favor of the strike authorization. This does not mean workers are hitting the picket line, however.

AFSCME District Council 33 is the largest union representing Philadelphia employees, covering over 9,000 members including sanitation workers. The union is looking for a long-term deal that includes salary increases while the city is looking for a 1-year contract extension.

Bus, trolley, and transit operators in the city are currently working without a contract. The last contract expired at midnight on Thursday, but union workers held off on a strike as both sides decided to continue negotiations. Meanwhile, on Friday, the union representing suburban transit workers formally voted to authorize a work stoppage.

The union that represents thousands of Philadelphia mass transit system workers has agreed to delay a potential strike, saying progress was being made in ongoing contract talks.

The three unions representing some of the city's most essential workers are all considering the same action: a strike.