Outsourced cleaners at HMRC tax offices in Liverpool struck over pay on 27 December.
The members of the PCS union are demanding bosses at private contractor ISS pay them a wage of £10 an hour.
They also want equivalent conditions to workers employed directly by HMRC.
Following strikes, ISS said it would ask HMRC for more money to meet strikers’ demands.
One striker said, “We’ve got no choice but to strike because cutting of hours and chronic low pay have driven many members into financial hardship.
“Only by staying united and strong can we finally force this cruel and ruthless employer to treat us with some dignity and pay us a living wage.”
Large Goods Vehicle driving examiners struck between 16 December and Christmas Eve. The PCS union members are involved in a long-running dispute with bosses at the Driving, Vehicle and Standards Agency (DVSA) over longer working days, staffing shortages and increasing workloads.
The strike follows a month-long walkout by IT workers in the DVSA in August.
The PCS said the action came after talks at conciliation service Acas broke down as “management refused to meaningfully negotiate with reps”.
Strikers braved wintery weather on solid, well?supported picket lines.
In Bredbury near Stockport, non-striking colleagues brought messages of support and hot food to those in the cold.
Other well-supported picket lines took place in Atherton, Greater Manchester, Shrewsbury, and Weedon in the East Midlands.
The action led to numerous cancellations of tests across the regions.