Senior Labour MPs have joined rail workers on picket lines across the UK, despite a reported warning from leader Sir Keir Starmer which banned his frontbenchers from the strikes.
Those from the more left wing of the party - MPs who held senior jobs under former leader Jeremy Corbyn - were out in force supporting workers but even some of Sir Keir's top team broke cover to join strikers.
Labour whip Navendu Mishra and Kate Osborne, a parliamentary aide to Shadow Northern Ireland secretary Peter Kyle both tweeted photographs of themselves on picket lines, describing themselves as trade unionists who "stand on the side of the workers".
It is not clear whether they will be punished but party leader Sir Keir is said to be considering possible disciplinary action for those who defy his order to avoid picket lines.
It was understood Sir Keir was waiting until the end of the industrial action before instructing chief whip Alan Campbell to deal with disciplinary issues.
It comes after the Politics Home news-site revealed a message apparently sent by the Labour party leadership to shadow cabinet members, warning them against attending the strikes.
"We do not want to see these strikes to go ahead with the resulting disruption to the public. The government have failed to engage in any negotiations," read the message.
It added: “However, we also must show leadership and to that end, please be reminded that frontbenchers including [parliamentary private secretaries] should not be on picket lines.
“Please speak to all the members of your team to remind them of this and confirm with me that you have done so.”
Labour did not say whether or not the MPs could lose their frontbench roles as a result, with a spokeswoman saying: “Unlike the government, our focus is firmly on the public.”
Former shadow home secretary Diane Abbott appeared to mock her leader's order, tweeting a photograph of herself at a picket line in London, adding in the caption: "(But don’t tell Keir Starmer)".
Party leader Sir Keir has sat on the fence over the strikes as he performs a difficult balancing act; supporting workers to get higher wages without seeming to support strike action that is severely impacting millions.
Instead of giving his unequivocal support to the strikers, as trade unions and many backbenchers want him to, he's insisting he does not want the strikes to go ahead and has blamed the government for refusing to negotiate.
But Deputy Leader Angela Rayner gave clear backing to the industrial action, tweeting: “Workers have been left with no choice.
“No one takes strike action lightly. I will always defend their absolute right to do so for fairness at work.”
Scottish Labour leader Anas Sarwar, who sits in the Scottish Parliament, distanced himself from Sir Keir’s position by heading to a picket line to show his “solidarity”.
“The workers don’t want strikes. The unions don’t want strikes. The public don’t want strikes,” he said.
There were several familiar backbench faces at picket lines who once held positions on the frontbench.
Former Shadow Chancellor John McDonnell was at a West Ruislip strike and Richard Burgon, previously the shadow justice secretary was picketing outside Victoria Station in the capital.
Ian Lavery, the MP for Wansbeck and a former Labour Party chairman, joined a picket in Morpeth, Northumberland, tweeting: “Solidarity with the @RMTunion today and all days.”
Former shadow cabinet minister Mr Burgon said: “We can’t just keep accepting workers’ wages and conditions being driven down so that the profits of the rich are driven up.”