The Ilford South MP defied orders from the party leadership not to join rail workers on the picket lines when they walked out on strike on Wednesday.
Mr Tarry also gave a series of unapproved media interviews in which he appeared to make up Labour policy on the spot, suggesting the party would grant rail workers an at least inflation pay rise if in Government.
Sir Keir’s tough approach to discipline in the aftermath of the incident sparked outrage among left-wing MPs.
Labour backbenchers lined up to attack the leader’s decision and accused him of failing to be on the side of workers.
Appearing alongside Mr Tarry this morning, former shadow chancellor John McDonnell appeared to call for other frontbenchers to shun Sir Keir’s stance on the strikes.
He said: “If you’re a Labour MP, whether on the frontbench or the backbench, you should be on the picket lines.”