Mr Tarry, MP for Ilford South, joined the workers and union members on Wednesday (27 July), despite Mr Starmer previously warning his MPs to stay away from the picket lines.
Rail workers participated in their second strike of the summer amid a pay dispute with Network Rail.
The Labour leader is set to visit Birmingham on Thursday (28 July) and attend the opening ceremony of the Commonwealth Games as the debate continues over Mr Tarry’s sacking.
Unite union, a financial backer of the Labour party, said his sacking “would be laughable if it were not so serious”.
Why was Sam Tarry sacked?
Mr Tarry attended the London Euston RMT picket line on Wednesday.
A Labour spokeperson has said that the MP had consequently been fired from his transport role after making media appearances without the party’s permission.
They said: “This isn’t about appearing on a picket line. Members of the frontbench sign up to collective responsibility. That includes media appearances being approved and speaking to agreed frontbench positions.
“As a government in waiting, any breach of collective responsibility is taken extremely seriously and for these reasons Sam Tarry has been removed from the frontbench.”
In a statement in regards to his sacking, Mr Tarry said: “It has been a privilege to serve on Labour’s frontbench for the past two years and to have had the opportunity to speak up for hard-pressed workers who deserve so much better than the treatment they’ve received from this corrupt and out-of-touch Government.
“I remain committed to supporting the striking rail workers, and campaigning for a Labour victory at the next general election, which I will fight for relentlessly from the backbenches.”
What did Sam Tarry say on the picket line?
While at London Euston, Mr Tarry told reporters at the picket line that “any labour MP” would have “absloute solidarity with striking workers”.
During a media appearance with the BBC while on the picket line, the former shadow transport minister said he was attending in his capacity of shadow transport minister.
He added that under a Labour government “this dispute would not take place” as they party would have already implemented a “fair pay deal”.
What has been the reaction to Sam Tarry’s sakcing?
Colleagues of Mr Tarry’s have shown solidarity with him for appearing on the picket line.
Labour MP Rachael Maskell tweeted: “Every @UKLabour politician should visit rail workers on the @RMTunion picket lines & listen to why they are asking for job security, better safety & decent pay. Labour politicians are in Parliament to be their voice. @SamTarry has shown leadership today ... a real Labour MP.”
Zarah Sultana added: “Labour MPs should be proud to stand with workers. The clue is in the name.”
Unite union, a financial backer of the Labour party, released a statement following Mr Tarry’s sacking.
Union general secretary Sharon Graham said: “The sacking of Sam Tarry for supporting working people on strike, against cuts to their jobs and pay, is another insult to the trade union movement. Quite frankly it would be laughable if it were not so serious.
“At a time when people are facing a cost of living crisis and on the day when the Conservative Government has launched a new wave of attacks on the rights of working people, the Labour Party has opted to continue to indulge in old factional wars.
“Labour is becoming more and more irrelevant to ordinary working people who are suffering. Juvenile attacks on trade unionists will do absolutely nothing to further Labour’s prospects for power.”
Former Labour deputy prime minister John Prescott tweeted a photo of himself addressing striking miners when he was shadow transport secretary in 1984.
What did Keir Starmer say about picket lines?
It comes after the party leader told his MPs to stay away from picket lines during the country-wide rail strikes and not to show support.
A leaked memo showed that the leader took the stance that the strikes should not go ahead, accusing the Conservative government of failing to resolve the dispute.
The memo read: “We must also 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.”
Despite this warning, some Labour backbenchers and junior frontbenchers have shown solidarity for the cause, including MP Diane Abbott who join the Seven Sisters station picket line during the last strike.
Scottish Labour leader Anas Sarwar also showed his support of striking workers by joining the picket line at Edinburgh Waverley station in July.