A long-serving Labor MP has slammed her party's preselection process which was seen her become a "victim" of a "cynical factional exercise".
South West upper house MP Adele Farina will lose her seat in Parliament at the next election after Labor's factions handed it to Regional Development Minister Alannah MacTiernan, allowing the left faction's Pierre Yang to take her safe seat in Perth's northern suburbs.
Mr Farina said she wasn't surprised the deal had been done.
"It is deeply disappointing to me to be deprived of my preselection for the South West after 19 years of faithful service and hard work in the electorate and Parliament," she said.
"The left faction does not believe that Mr Yang, despite the huge popularity of the Premier and the government and Mr Yang’s recruiting efforts, will be able to hold his current seat.
"It is particularly disappointing that preselections have been rushed through the administrative committee five days before the party resumes normal business after the COVID-19 restrictions."
Ms Farina said the party's rank and file members had been denied a say in the preselection.
The long-serving MP took aim at Ms MacTiernan, who was first elected to State Parliament in 1993.
"It is personally disappointing Ms MacTiernan, whom I have strongly supported throughout her career, and who has campaigned for party rank and file participation in preselections and against this kind of deal-making by faction leaders, has willingly been involved in this cynical factional exercise," she said.
"Despite my disappointment, I accept the decision of the administrative committee and will continue my hard work representing the people of the South West for the remainder of my Parliamentary term.
"The South West has been my life. I have given it 100 per cent. It deserves nothing less."
Ms Farina attracted the ire of her left-wing colleagues when she voted against the government's euthanaisa legislation.
She was elected to Parliament in 2001.