The United Firefighters Union (UFU) has pulled out of the Victorian Trades Hall Council amid claims it has been bullying Labor MP Jane Garrett.

Ms Garrett, a former emergency services minister, has been embroiled in a stoush with the UFU in what union secretary Peter Marshall says is a campaign to undermine firefighters.

She says she has been bullied by the union during industrial negotiations.

Ms Garrett, the Member for Brunswick, plans to vacate her seat to contest an Upper House position, pending the outcome of Supreme Court challenge against her preselection, which was instigated by another UFU member.

Another major Victorian union has called for the “relentless bullying” of Ms Garrett to stop.

“This matter is one we as a movement, can no longer stay silent on,” said secretary of the Rail, Tram and Bus Union (RTBU) Luba Grigorovitch.

“The RTBU has always maintained a working relationship with Peter and the UFU, but it's time that this relentless bullying and attacks come to an end.”

Construction, Forestry, Maritime, Mining and Energy Union (CFMEU) boss John Setka has labelled the court challenge petty.

“What's happened to Jane is just totally unacceptable and I think people have just got to sort of sit around a room and really get over it,” he said.

CFMEU assistant secretary Shaun Reardon wrote to Premier Daniel Andrews earlier this year to try to stop the personal attacks on Ms Garrett.

“I implore you to stand strong on party matters with any undertone of misogyny or workplace bullying and to continue your outstanding work in relation to violence against women,” his letter read.

The Trades Hall has conceded it is rare for a union to leave the council, and that it expects the move to have practical and symbolic consequences.

Mr Andrews has affirmed his support for Ms Garrett, but stopped short of criticising the UFU's move.