Le Regroupement des activistes pour l'inclusion au Québec (RAPLIQ) said people with reduced mobility are extremely limited in their access to Montreal's trains, metros and buses.
Lawyer Aymar Missakila said he'll be seeking $5,000 in damages for up to 20,000 possible plaintiffs.
"We've waited too long to be considered real citizens," said Linda Gauthier, president of RAPLIQ.
"Our rights are guaranteed in Quebec and Canada's Charters of Rights and in the International Convention on the Rights of Handicapped Persons, which Canada ratified in 2010," Gauthier said.
The group said only four of the 13 new stations on the AMT's new Train de l'est commuter train line are accessible, and only one station out of 51 on the AMT's five other lines are accessible.
It noted only eight of the STM's 68 metro stations are accessible, and that the STM's fleet of accessible buses is plagued by mechanical problems.
RAPLIQ said the provincial transport ministry has cut funding to the transit agencies for accessibility programs.
The group also blamed politicians at city hall for not taking the issue seriously.
"We rely on public transit to live our lives every day, to be economically and socially successful, and we are undermined every day," said RAPLIQ member Laurent Morissette, who uses a wheelchair.
"We often have to wait on sidewalks in freezing temperatures while other people live their lives. We are left waiting on the sidewalk of life," said Morissette.
The class action will need to be approved by the court before it can proceed.