Mometum wants Lord Mandelson to be stripped of the Ġieħ ir-Repubblika award after he was outed in the Jeffrey Epstein files.
Lord Mandelson was sacked from his position as Ambassador to the USA last September when further details about his relationship with Epstein were made public, Momentum said.
Last Sunday, he also resigned his Labour membership after four decades as one of the leading figures in the party.
And now he has had to resign from the House of Lords.
In 2016, with the intention to curry favour with EU leaders, Joseph Muscat bestowed Ġieħ ir-Repubblika on Mandelson.
Arnold Cassola stated 'Now that we know what backroom deals Mandelson was involved in, Momentum shall be writing to the Ġieħ ir-Repubblika committee to strip Mandelson of the honour which Joseph Muscat had decided to bestow upon him. Malta must exercise significantly greater due diligence when conferring state honours to ensure recipients are of unimpeachable character."