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.

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.

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.

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.

While both unions have authorized strikes, there is no sign either union is ready to hit the picket line just yet. Neither union has declared a strike deadline.

The transit agency is negotiating contracts between TWU Local 234, which represents workers in the city, and SMART Local 1594, which represents workers in the suburbs.

SEPTA riders should have a plan just in case the workers in the suburbs decide to strike Monday night. Services could be impacted as early as Tuesday.