Hundreds of binmen in Birmingham walked out after two colleagues were suspended, a union said.
Binmen were on strike over pay on 20 December and have been working to rule since. The city council has hired 200 casual staff to cover.
It said the suspensions followed a collection vehicle being blocked in and prevented from carrying out duties.
Paul Langley, of the GMB, said about 500 to 600 workers walked out on Thursday, but were now back at work.
He said: "We had a phone call saying that our dustmen at Birmingham City Council, our colleagues, were being suspended for an incident that happened with agency staff.
"So we decided to support our lads and walk out... because we're not being treated equally as these are.
"If something like this happens, they should have been suspended as well."
In an earlier statement, the council said: "There was an incident involving one of our collection vehicles being blocked in and prevented from carrying out their duties, which has resulted in the suspension of two employees.
"The council will not tolerate inappropriate behaviour from either permanent or temporary staff and will take the appropriate action."
The bad weather and the Christmas break has led to a backlog of binbags left on streets.
The GMB said about 800 people were on strike on 20 December.
The pay dispute centres on proposals to address a pay gap between male and female colleagues employed by the council which Unite has said amounted to a £4,000 pay cut.