Pan-democrats favour "public nomination" of candidates for the chief executive election in 2017.
But some pragmatic members of the camp, realising the ultimate power of the nominating committee to decide the final candidates, are more concerned about how the committee decides on which candidates will go to the popular vote.
They believe the committee should adopt the "one man, one vote" system when deciding on the candidates.
Qiao Xiaoyang , chairman of the National People's Congress Law Committee, said in March that the nominating committee might make a collective decision on candidates.
But pan-democrats fear this could see their candidate being screened out.
The practice would be a departure from that adopted in the 2012 chief executive election when an aspirant only needed to secure the nomination of 150 of the 1,200 members of the Election Committee to enter the race.
Under public nomination, any registered voter could nominate a candidate, who would then have to be endorsed by a certain number of people before being put forward to the committee. Eleven out of 27 pan-democratic lawmakers have signed a charter prepared by student-led group Scholarism promising to fight for public nomination.
But to the Democratic Party's Dr Law Chi-kwong, the bottom line is whether a pan-democrat candidate can join the election.
He said if voters could nominate so-called pre-candidates and the nominating committee adopted the one-man, one-vote system to vet them, that may be an acceptable solution for residents and would not violate the Basic Law. "You also have to expand the nominating committee to maximise citizens' participation," Law said.
The Basic Law says chief executive candidates must be nominated by a "broadly representative" nominating committee in accordance with "democratic procedures".
Bruce Liu Sing-lee, chairman of the Association for Democracy and People's Livelihood, said the block-vote system, under which the number of votes cast by each nominating committee member would be equal to the number of candidates shortlisted for popular vote, was unacceptable.
The block-vote system is used in the election of Hong Kong deputies to the National People's Congress. No candidate from the pan-democratic camp has been returned since 1997.
Basic Law Institute chairman Alan Hoo has proposed adopting block voting in an expanded 1,500-strong committee.
But Dr Ma Ngok, a political scientist at Chinese University, said it was hard for the pan-democrats to support blockvoting as it was vulnerable to manipulation.
"As long as you hold the majority of seats in the nominating committee you can easily manipulate the final list of chief executive candidates," Ma said. "The chance of pan-democrats being admitted as candidates would become even slimmer."