More than 200 MUA members rallied in Fremantle on Wednesday outside a briefing by the Westport taskforce, which has backed Labor's election promise to build the new facility.

The union, which fears automation will cost 8000 jobs, also marched to the electorate office of Labor minister Simone McGurk, who helped vote down an MUA-led motion to keep Fremantle Port operational for a further 14 years at the party's shambolic state conference last month.

The union said the protest was "sometimes loud and boisterous", but Mr McGowan told parliament some of the tactics were threatening, bullying and disgraceful, and social media posts had prompted death threats against him.

One of them was a complete lie, he said.

After MUA national president Christy Cain claimed on Facebook Mr McGowan had received a 12 per cent wage rise, commenters called him "McGrub", "d***head", "maggot", "parasite", "back stabbing scum" and "piece of s***".

"This is part of the reason I'm no longer a Labor member. I will be searching for a new party," a wharfie posted.

Mr Cain later posted: "Just heard that 6PR have reported this wrong and McGowan is not getting a pay rise now. Probably because he is on too much anyway!"

Simmering factional tensions within Labor erupted at the state conference when the MUA and CFMEU walked out during a welcome to country and a tribute to former prime minister Bob Hawke.

It was sparked by an unsuccessful move to disqualify a delegate, who is a member of the MUA and did not meet sign-up requirements, leaving Mr McGowan to deliver his keynote speech to a largely empty room.

The MUA and CFMEU joined the right-leaning Progressive Labor faction, which has sought to challenge the dominant left, in 2017.

The MUA abandoned its decades-long affiliation with UnionsWA, which is on the left, after the conference.

Australian Associated Press