Local 225 of the Transport Workers Union of America failed to reach a contract with Hudson Transit Lines. Workers rejected a revised three-year pact Thursday by a margin of 101 to 89.
The strike is the first since 1987 and will affect thousands of Short Line customers in New York, New Jersey and Pennsylvania - including many commuters to New York City.
The union represents about 240 drivers, mechanics and ticket agents.
Picket lines were expected Friday at facilities in Mahwah, Montgomery, Binghamton and the Port Authority.
Company officials said in a prepared release that the union rejected a "generous contract" that included 4 percent annual raises. They encouraged strikers to return to work.
In response to the strike, Metro North Railroad and New Jersey Transit are both offering additional service.
