Truck drivers who work at the ports of Los Angeles and Long Beach walked off the job Thursday to protest two trucking firms they accuse of wage theft, according to the International Brotherhood of Teamsters, which organized the action.

The picketing in protest of Total Transportation Services Inc. and Pacific 9 Transportation is the fifth labor action in about a year. It’s not clear how many drivers walked out Thursday.

In July, the union launched an “indefinite” strike. But after five days of picketing, Los Angeles Mayor Eric Garcetti brokered a cooling-off period. Part of the deal was a stipulation that all drivers would be allowed to return to work without retaliation, according to the Teamsters. On the Thursday morning, drivers said the two companies in question did not honor this agreement.

In a statement, Mayor Garcetti said that TTSI had agreed to speak with the Teamsters at the Mayor’s office to “find a way to get its operation back to work.” He urged Pacific 9 to do the same.

“It is in everyone’s best interest for these operations to continue,” Garcetti said.