Labour MP Sue Moroney has announced her retirement from politics - a day before the expected release of the party's list rankings.

Moroney said she had been told last night she had lost support from the party's ruling council for an electable position on the list ahead of September's election.

Labour had already confirmed its candidates to run in all 71 seats, and Moroney's decision means it will need to hold a new selection in Hamilton West, where she was to have run.

Moroney, who entered Parliament in 2005, said she would serve out the remainder of the Parliamentary term.

"I am grateful that I have had the opportunity to fight for the rights of children, working families, women and the people of Hamilton.

"I'm proud to have extended paid parental leave, achieved mandated meal breaks and rest periods for workers and fought early childhood education cuts amongst other things."

Moroney said she looked forward to spending more time with her family and friends, and to "plan the next chapter of my life in pursuing equality and social justice".

The overall percentage of party vote and number of seats won determines how many candidates are elected from a party's list.

Labour is expected to announce its list rankings tomorrow, National in late June or July. Neither Prime Minister Bill English or Labour leader Andrew Little are contesting electorates and will be number one on their party's list.