Three losers in last December's provisional legislature selection will contest the seat vacated by Maria Tam Wai-chu following her appointment to the Basic Law Committee.
Ms Tam wrote to the president of the interim body, Rita Fan Hsu Lai-tai, yesterday to tender her resignation.
The case has already been referred to the Preparatory Committee Secretariat.
It will have to call a meeting of the 400-strong Selection Committee to pick the replacement for Ms Tam, unless two contenders decide to quit the race.
Originally, the Preparatory Committee's regulations on the selection method said any vacancy should be filled by the highest scorer of the 70 losers.
But three losers - including National People's Congress deputy Peter Wong Man-kong, defeated Legco candidate Choy So-yuk and unionist Leung Fu-wah - managed to win 162 votes, leaving them all in 61st place.
