Pro-democracy groups are threatening a campaign of "passive resistance", including class boycotts by university students, if Beijing rules out allowing the public to nominate candidates for chief executive in 2017.
The action plan was agreed last night at a meeting involving pro-democracy groups and student organisations.
But a co-organiser of the Occupy Central campaign said its plan to block streets in the heart of the city could be averted if Beijing allowed the committee that picked candidates to be formed democratically.
Johnson Yeung Ching-yin, convenor of the Civil Human Rights Front, said the groups would consider small-scale localised protests if, as expected, the National People's Congress Standing Committee ruled out public nomination next month.
"We will certainly take action to respond if Beijing does not respect the will of those 800,000 people who came out to vote in the civil referendum," said Yeung, referring to a poll last month on electoral models for 2017, organised by Occupy.
But Dr Chan Kin-man, an Occupy co-organiser, said a decision to rule out public nomination would not, in itself, trigger the group's threatened civil disobedience protest.
"We shall look not only at whether there is public nomination, but also at how Beijing or the [Hong Kong] government deals with the formation of the nominating committee. For example, if all nominating committee members are elected by the public, I believe the public will be willing to consider it. So we will have to look at the NPC Standing Committee decision first."
Meanwhile, moderate pan-democrat Ronny Tong Ka-wah said different views of the likely outcome of a collapse in the electoral reform effort were clouding the chances of a deal.
Tong said Beijing believed pan-democrats would suffer at the ballot box if they scuppered a reform proposal, which would require a two-thirds majority in the legislature. But pan-democrats believe they will benefit if Beijing is seen as inflexible.
Tong's remarks came as 18 pan-democratic lawmakers asked Chief Secretary Carrie Lam Cheng Yuet-ngor to help set up meetings with Beijing on reform.