The half-day action by up to 400 workers in the West Midlands caused postponement of hundreds of court cases across the region, two days before the government was due to unveil the criminal justice reforms which form the main plank of this year's Queen's speech.
Members of AMO, the union for magistrates court staff, are angry at a pay harmonisation scheme which will lead to pay cuts for about a quarter of workers.
The union wants compensation for members facing a pay cut, as well as back pay for those whose pay will rise. Rosie Eagleson, the AMO's general secretary, said: "Hundreds of members are on strike and I would estimate that well over half the courtrooms in the region are not operating.
"I hope the message gets through to the government that modernisation does have a cost and they cannot expect our members to pay for it out of their wage packets."
A spokesman for the Lord Chancellor's Department said any dispute was a matter for the West Midlands magistrates courts committee, the independent body which runs the courts. The committee said 43 out of 76 courts were sitting yesterday morning.
The justices' chief executive, Alan Eccles, said: "The committee is working to reach an affordable solution to achieving fair pay for all our staff across the region."
