Staff at six prisons staged a brief walkout in protest at the suspension of two prison officers, their trade union said.
The Prison Officers' Association said hundreds of staff at Lindholme and Moorlands prisons near Doncaster, South Yorkshire, and at Everthorpe prison in East Yorkshire walked out at lunchtime.
They said strikes followed at Wakefield, Hull and New Hall prisons - a claim disputed by the Government.
Prison staff returned to work after prisons management agreed to review the suspensions of two officers, the POA said.
The Ministry of Justice said no more than 200 officers left their posts. A spokesman said the second three walkouts were in fact staff holding meetings during breaks.
He said: "This industrial action by members of the POA was simply unacceptable. By taking this action they put the safety of the public, staff, and the prisoners at risk.
"When staff are suspended pending disciplinary action, there is a clear process for the individual(s) to lodge an appeal supported by their trades union."
Tom Jones, POA chairman at Lindholme said the dispute was "not just about disciplinary matters but also about the thousands of hours of unpaid work that the prison officers here have done".
The walkout came after two officers were suspended at Lindholme over evidence they gave at a disciplinary hearing, the POA said.
They were accused of failing to tell the truth about an incident in which a female prison officer was alleged to have assaulted a male prisoner.
