Fifty-four members of the Iranian parliament pledged Thursday not to take part in next month's parliamentary elections if the poll does not give voters a free choice of candidates.
AFP correspondents said the 54 were continuing to collect more signatures to their commitment among reformist colleagues in the 290-seat parliament who are facing wholesale rejection by a conservative candidate-vetting body.
They also vowed in their statement not to sit in the outgoing parliament between the February 20 elections and the opening of the new assembly in June, potentially paralysing the legislature for months.
"We, representatives of the people, swear that if the rights of the candidates in the legislative elections are not guaranteed we will not take part in elections where the free choice of voters is trampled," the statement said.
"We bind ourselves not to sit in parliament ... if the elections amount to nominations," it added.
The 12-member Guardians Council which screens all legislation and candidates plunged Iran into one of its most serious crises when it disqualified 3,605 of the 8,157 people seeking to stand for the parliament, or Majlis.
Most were reformists, including prominent figures in the reform movement close to President Mohammad Khatami and some 83 incumbent MPs.
Supreme leader Ayatollah Ali Khamenei last week ordered the council, all of whose members he directly or indirectly appoints, to be less stringent in its vetting procedure.
The council has since reinstated some 300 candidates, but none of them were sitting MPs.
On Sunday, 18 reformist parties in a coalition said in an open letter to the president they would decide Thursday whether to boycott the election.
The coalition said it would make its decision based on the extent of the Guardians Council's review process.
Dozens of reformist MPs have been staging a sit-in protest at the parliament since January 11 when the Guardians Council issued its blacklist, triggering charges of an attempted "coup" in the Islamic republic.
According to Tehran newspapers, five of Iran's vice presidents, including Massumeh Ebtekar, and six ministers, including Interior Minister Abdolvahed Mussavi-Lari, have handed in their provisional resignations.
The Guardians Council has until January 30 to inform the interior ministry, which is in charge of organising the polls, of the final approved list of candidates.