Labour MPs have begun urging party leader Jeremy Corbyn to step in and order an emergency meeting of the National Executive Committee to review the decision not to expel former London mayor Ken Livingstone for comments about Hitler and Zionism.

Tulip Siddiq, MP for Hampstead and Kilburn, was one parliamentarian reacting in anger to a decision by the party’s National Constitutional Committee, which found Livingstone guilty of bringing the party into disrepute but stopped short of expulsion.

She said the NCC’s decision to suspend Livingstone for two years, conveyed on Tuesday, was “intolerable” and “brings great shame on our party”.

Siddiq, who is vice-chair of the All-Party Parliamentary Group Against Anti-Semitism, said: “What should have been an open-shut disciplinary case has become a year-long insult to a community that I am so proud to represent.”

She said the decision was “desperately disappointing” for her Jewish constituents, “as it was for all those dedicated to anti-racism in our movement… Members have contacted me in despair over the past twelve hours. They have seen this as the final straw and have terminated their membership”.

In a letter to Corbyn, who has so far refused to comment, Siddiq said she believed “many more” Jewish Labour members would leave the party “unless we act swiftly”.

She added: “I believe the insufficiency of the punishment means that the Party must explore all options available to it. This includes asking the National Executive Committee to convene an emergency session to review the decision.”

The NCC is the party’s ultimate decision-making body, and considered Livingstone’s case after the NEC referred his case. Three NCC members, whose identities remain secret, considered the matter over a two-day hearing last week.