West Australian Shop Assistants czar Joe Bullock is set to assume the top spot on Labor’s WA senate ticket — consigning sitting Senator Louise Pratt to a potentially dicey number two position — when the party’s state executive meets on Monday to rule on her future.

And in a bitter blow to the party’s “blue collar blokes” faction, Crikey understands delegates aligned to “soft Left” trailblazers United Voice will honour the terms of a deal to round behind Bullock and deliver Chris Evans’ Senate vacancy to United Voice assistant national secretary Sue Lines.

While the number two position is usually considered safe, and will probably be held again in September, a further plunge in Labor’s primary vote from an already low base could end up forcing Pratt to the curb.

The 175-strong state executive is split between about 100 Left and 75 Right delegates. The Left is in turn split 50/50 between the Pratt-supporting blokes on the one hand (the Australian Manufacturing Workers’ Union, the Maritime Union of Australia and the Electrical Trades Union) and United Voice on the other. The Right comprises the dominant Shop Assistants union, the Transport Workers’ Union and the Australian Workers’ Union.

One side of the Left can therefore coral the Right to roll their internal rivals — this is exactly what’s happened this time around.

Thanks to a 14-month-old deal hatched between United Voice and the WA Shop Assistants during the Fremantle preselection, state executive is almost certain to vote up Bullock at number one, Pratt at two and consign Mark Bishop to premature retirement.

The simmering rancour, first highlighted by Crikey in February, has now exploded on Facebook, with Pratt tapping out a wall post yesterday to slam suggestions she had attempted to hatch her own deal with Bullock — presumably to deliver him Evans’ spot, install an SDA acolyte as WA upper house leader and knife United Voice-aligned state secretary Simon Mead.

But Pratt instead unloaded on Bullock, haranguing the socially conservative union leader for his “anti-marriage equality” stance and his objections to a “woman’s right to control her own body”.

Under the traditional factional arrangement carve-up of the four winnable WA Senate seats is one SDA, one “rest of the Right”, one United Voice and one “rest of the Left”, usually Pratt’s AMWU. But WA Labor’s declining primary vote has led to some amusing shenanigans epitomised by election night hijinks in 2010 when Senator Glenn Sterle was texted alternative job offers at 9.30pm as the disappointing vote trickled in.

Still, for Pratt to lose from number two, Labor would need to fall below 28.6% on the primary vote, which no major party has ever done. If the Greens vote falters, Scott Ludlam would drop out and Pratt would get elected on Greens preferences, leaving four Tories and two Labor.

One senior Left source explained the Pratt situation and its Fremantle roots thusly: “All of this is a mirror of what happened 14 months ago. [MUA national secretary] Paddy Crumlin was running around demanding that [MUA state deputy secretary] Adrian Evans be the candidate for Fremantle. Paddy ran a very strong national campaign saying this is our man and this is our seat and he needs to be installed.”

“They were going to step out of the Left and get the Right to vote for them. All the national secretaries were all on board.”

United Voice instead hatched an agreement with Bullock to vote for the endorsed Left candidate, Simone McGurk, who became the candidate after the “blue collar blokes” absented from the decision. As a quid-pro-quo for that vote the Left agreed to back Bullock on Monday.

“This was about getting a progressive Left woman into Fremantle, and Joe voted for it. And now Joe wants to be number one in the Senate, and that was the deal. All the running around that’s happening now is ignoring the fact that 14 months ago there was a stupid threat to an amazing woman who’s going to be a senior minister one day by some really aggressive blokes and they played pretty dirty and they lost and now they’re screaming that Louise Pratt might end up at number two,” they said.

“The deal still stands. The first leg of the deal is complete and the second leg of the deal will go down on Monday. ”

The senior source attacked Pratt’s social media intervention: “Louise is right in saying that no deal has been done. She’s absolutely right, Joe rejected them outright. The fact that they were shopping it around for a month appears to have slipped her notice in her Facebook post.

“There are no good guys in this. It’s all shit. And it’s going to fall apart after Monday,” they added, alluding to a looming factional rearrangement that is likely to benefit the blokes.

MUA state secretary Christy Cain has pledged to seize control of the state party, writing in today’s West Australian that Labor should be run by people that work with their hands. The union is vigorously recruiting Labor members before the new state executive is divvied up in 8 weeks time. When the spoils are allocated, the industrial left is likely to command a left caucus majority.

Pratt didn’t return calls this morning.