A pair of influential union leaders have rounded on Kevin Rudd's call for the full democratisation of the ALP, accusing the former prime minister of being "angry and bitter" and arguing Labor has benefited from his absence from political debate.

On Tuesday, Mr Rudd he called for the "full democratisation" of the Labor Party and lashed the "thuggery" of factional bosses who removed him in 2010.

Former prime minister Kevin Rudd. Credit:Andrew Meares

Mr Rudd criticised a proposal from Transport Workers Union boss Tony Sheldon and Rail, Tram and Bus Union boss Bob Nanva to give unions a one-third say in selecting the federal Labor leader, with the other two-thirds evenly split between the caucus and party rank-and-file, which would alter reforms the former prime introduced in 2013.