Keir Starmer is under pressure over his stance on Labour MPs joining picket lines after a shadow minister defied orders not to join the striking workers, saying he was “on the side of the members not the establishment”. The Labour leader is now facing a dilemma over whether to sack the shadow transport minister Sam Tarry, who joined rail workers outside Euston station in London. Senior Labour sources alleged one of Tarry’s motives was to make a stand in order to help with his local constituency selection battle – where he is facing being deselected in Ilford South. Starmer has told shadow ministers not to join picket lines, stressing that Labour is a party of government that should aim to solve disputes. Several shadow ministers who joined picket lines during the last strike did not lose their jobs, despite the warning. Tarry, a former officer of the TSSA trade union who helped run Jeremy Corbyn’s leadership campaign, has not previously joined the picket lines as a shadow minister, though he tweeted a picture of himself alongside workers on an earlier strike day. Ruth Jones, a shadow environment minister, has also posted pictures supporting the strike. One shadow cabinet source said they believed Starmer’s position on picket lines would become unsustainable as the number of disputes intensified – with potential strikes planned by postal workers, NHS staff and teachers. “There will be other frontbenchers who will want to support striking workers in their constituencies,” they said. Tarry told ITV News it was not his intention to defy Starmer and said the disputes would not be happening under a Labour government. “I’m here supporting these striking workers because it’s important we get a pay deal and get to resolve as soon as possible so the travelling public can get back to work,” he said. “The reality is this is about a failing government, this is about dispute happening all across the country. We’ve got potentially doctors, nurses and communication workers.” Advertisement Tarry said: “No one said anything to me about whether or not I should be on a picket line today.” A Labour source said the advice from party whips not to join picket lines had not been reissued since the first strikes but was still party policy. Asked whether he expected to be sacked, Tarry said: “If Labour were in power and I was secretary of state for transport this dispute would not be happening.” Other shadow ministers have not been sacked for attending picket lines, though Tarry is the first to do multiple broadcast interviews from the strikes. Senior Labour sources said they were sceptical of Tarry’s motives and linked it to his reselection battle in Ilford South. Wards in Tarry’s constituency voted unanimously for a full reselection – meaning he is likely to lose the seat. They suggested Tarry was in effect daring Starmer to sack him. One said: “He didn’t go to the first picket but has turned up now. So what has changed?” Tarry said after the interviews that he remained on the side of the striking rail workers, tweeting a photo that said he was “on the side of the members not the establishment”. He has previously written to Labour’s general secretary, David Evans, suggesting he had seen evidence of voting irregularity in his selection battle. Tarry won selection in the east London seat in 2019 after the local council leader, Jas Athwal, was suspended from the party in the run-up to the vote, over allegations of inappropriate behaviour. Athwal, an ally of the neighbouring MP Wes Streeting, was subsequently cleared in an internal investigation. Tarry’s is one of a series of potential trigger ballots under way, with leftwing Labour MPs also calling for the reselection process against Apsana Begum in Poplar and Limehouse, east London, to be suspended on the grounds of alleged misconduct by party members. Labour has not responded to requests for comment.