Iranian reformers have warned they may refuse to organise parliamentary elections due to a row over candidates.
The Guardians Council has disqualified some sitting MPs
A spokesman for reformist President Mohammad Khatami insisted on "fair competition for all the candidates".
"Without such a possibility... we cannot go ahead with such elections," spokesman Abdollah Ramezanzadeh told Iran's student news agency ISNA.
Reformists are furious the conservative Guardians Council has barred more than 3,000 candidates from the ballot.
On Sunday the powerful council rejected a legislative effort to overturn the ban on nearly half the candidates - including some sitting MPs - in the 20 February elections.
Analysts say MPs must now decide whether to submit the bill to a higher authority.
The Expediency Council, headed by former president Akbar Hashemi Rafsanjani, is meant to mediate in disputes between the parliament and the Guardians Council.
Reformists have said that they would boycott an election in which more than a third of candidates were prevented from running.
The unelected 12-member Guardians Council, which vets candidates for office, reinstated about 350 of the banned candidates after Iran's supreme leader, Ayatollah Ali Khamenei, ordered a review.
IRAN'S REINS OF POWER
Supreme leader Ayatollah Ali Khamenei: Appointed for life, overrides all other authorities (pictured above)
Expediency Council: Set up to mediate in disputes between the Guardians Council and parliament
Guardians Council: Half chosen by Khamenei, responsible for vetting election candidates and laws
President Mohammad Khatami: Elected for four years, power can be circumscribed by clerics
Parliament: 290 members introduce and pass laws, subject to approval
Students are also planning to organise mass protests to denounce hardliners.
"Students will join professors of all universities in Tehran today to support disqualified prospective hopefuls and denounce hardliners who are restricting people's choice," said student leader Hossein Baqeri.
Reformist MP Mohsen Armin said the Guardians Council had shown that it had no will to resolve the crisis logically.
"It only pushes reformist MPs to harden their position and seriously consider mass resignations and boycotting the polls," he said.
The Guardians Council set off what correspondents say is Iran's worst political crisis for years when it barred more than 3,500 mostly reformist candidates from the election.
Under the bill put forward on Sunday, those approved for past elections would have been able to run again unless there was strong evidence to prove they were unfit.
Mr Khatami, a reformist, has hardened his stance on the row.
On Saturday, he issued a joint statement with parliamentary speaker Mehdi Karrubi demanding that the Guardians Council make a "full review" of their blacklist.
The Guardians Council has promised to check all the disqualifications and issued revised judgements by 30 January.