Former Labor minister and Australian Council of Trade Unions (ACTU) president Martin Ferguson has attacked the level of union influence in the party, saying too many Opposition MPs "wait for the phone call from the trade union heavy to tell them what to do".

Key points: Former Labor minister says unions wield too much power in ALP

Former Labor minister says unions wield too much power in ALP Mr Ferguson says too many Labor MPs "prisoners" of union movement

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Mr Ferguson said Opposition Leader Bill Shorten did not have the power to curb union influence in the Labor Caucus without the backing of the shadow ministry.

"But at the moment I don't think that's possible," Mr Ferguson told Four Corners.

"Because too many of that shadow ministry and the Caucus are almost as if they're prisoners of the union movement." [sic]

Unions have significant influence over preselections for both Senate and Lower House seats in the Parliament, Mr Ferguson said.

"It's almost as if they sit down now and divide the cake, you get that seat, we get that seat, left and right together and they dole out the prizes to their faithful."

Mr Ferguson's attack comes as the ACTU and other unions moved last week to shut down the trade union royal commission after it was revealed Commissioner Dyson Heydon accepted an invitation to speak at a Liberal Party fundraiser.

Mr Heydon said he overlooked the connection to the Liberal Party and pulled out of the event when he realised it was a fundraiser.

Mr Heydon, who was appointed by the Abbott Government, will decide this week whether he will stand down on the grounds of a perceived bias.

Ferguson supports royal commission and hopes for Labor reform

Breaking ranks with his Labor colleagues who have described the royal commission as a "political witch hunt", Mr Ferguson backed its work, especially its investigations into the scandal ridden Health Services Union (HSU).

Sorry, this video has expired Cesar Melhem says he hopes he is not a "sacrificial lamb" after resigning as Upper House whip.

"I will not damn it," Mr Ferguson said.

"I think it's potentially going to be very important in reforming the trade union movement and the Labor Party."

Mr Shorten appeared as a witness before the royal commission last month and was questioned about his time as secretary of the Victorian branch of the Australian Workers Union (AWU), including agreements where workers were allegedly disadvantaged.

Mr Shorten's successor as head of the Victorian branch of the AWU, Cesar Melhem, told the program he hopes he is not "a sacrificial lamb" for his former union colleagues after he resigned as Upper House whip in the Victorian Parliament following controversy over his evidence to the royal commission in June this year.

"If I'm going to be the sacrificial lamb and save everyone else, well so be it, but I don't believe so," he said.

Mr Ferguson's comments backing the royal commission are likely to reignite calls by some of his Labor colleagues for him to be expelled from the party.

Just last month he avoided expulsion after several unions accused him of disloyalty.