The US transportation department said 3,700 employees had been temporarily furloughed after Congress failed to reauthorize surface transportation programs before a deadline that expired early on Friday.

A department spokesperson said the agency is “taking every step we can to mitigate the impacts of this temporary lapse in authorization” of the Highway Trust Fund.

Safety-critical employees are exempt from the furloughs. Aides said US lawmakers are considering a 30-day surface transportation extension as negotiations continue over a pair of infrastructure and spending bills.

The American Association of State Highway and Transportation Officials (AASHTO) said on Friday that $50 billion of federal surface transportation programs supported by the Highway Trust Fund are being suspended.

“It lapses our highway, transit, and highway safety programs and halts work on vital transportation infrastructure around the country, which is detrimental to our economy and the quality of life of our communities,” Jim Tymon, AASHTO’s executive director, said in a statement. “This is unacceptable.”