New Jersey Transit’s engineers union said late Thursday that they would go on strike at midnight after negotiations with state leaders broke down without an agreement.

The walkout by members of the Brotherhood of Locomotive Engineers and Trainmen would shut down New Jersey Transit’s rail network, leaving tens of thousands of commuters scrambling for other ways to reach their jobs in the New York City metropolitan region.

The union said its members would start picketing at 4 a.m. on Friday.

Mark Wallace, the union’s national president, said: “They have money for penthouse views and pet projects, just not for their frontline workers. Enough is enough. We will stay out until our members receive the fair pay that they deserve.”

About 70,000 commuters ride the agency’s trains to Pennsylvania Station in Manhattan on a typical weekday. Many thousands more ride trains to stations in Newark and Hoboken, where they transfer to other trains, buses or ferries.

NJ Transit’s statewide bus system would continue to operate as scheduled, and the agencyhas hired private buses to substitute for its train service. But Kris Kolluri, the chief executive of NJ Transit, warned that the chartered buses could accommodate only about 20 percent of the displaced train riders. Those chartered buses do not start until next week.

They would run from four Park & Ride lots around the state: Secaucus Junction; PNC Bank Arts Center in Holmdel; Hamilton Rail Station; and Woodbridge Center Mall.