Iran's interior minister has warned that elections may not be held, due to a row between reformers and hardliners.
Khatami says even a single ban is unacceptable
The minister told reporters it would be "out of the question" to hold the elections after conservatives barred thousands of candidates from standing.
"The possibility of organising a free and competitive election does not exist", Abdolvahed Moussavi Lari said.
The hardline Guardian Council reversed its decision to ban many candidates on Friday, but about 2,500 remain barred.
The bans have drawn daily protests from reformist MPs, 80 of whom had been disqualified from standing for re-election, and a boycott threat from a student group.
Reformist MPs began circulating and signing letters of resignation on Saturday, the AFP news agency reported.
President Mohammad Khatami had been trying to reach a compromise with the Guardian Council - an unelected 12-member body that vets candidates for office and all laws.
But that compromise appears decidedly one-sided, says the BBC's Miranda Eeles in Tehran.
Mr Khatami was admitted to hospital on Saturday suffering from severe back pain, forcing the postponement of an emergency government meeting that was to have discussed the election crisis.
Earlier, the state news agency Irna quoted him as saying his government "will only organise free and competitive elections".
Guardian Council member Reza Zavarei said the law required the interior ministry to hold the elections "on the legally appointed date", the Iranian student news agency ISNA reported.
Mr Lari had requested the postponement of the poll - scheduled for 20 February - but the Guardian Council said it saw no reason to do so.
IRAN'S REINS OF POWER
Supreme leader Ayatollah Ali Khamenei: Appointed for life, overrides all other authorities (pictured above)
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
On Friday, the Guardian Council said it had reversed bans on a third of the candidates initially barred.
The body originally disqualified about 3,600 of 7,900 candidates.
The Guardian Council had already reinstated several hundred candidates, following a call for a review by the Supreme Leader, Ayatollah Ali Khamenei.
The latest reinstatements bring the official number of candidates to about 5,450.
On Thursday, Iran's provincial governors complained that there were not enough candidates for a free and fair election.
Earlier, Iran's main pro-democracy students' group, the Office for Fostering Unity, called on people not to vote.
The groups also urged reformist MPs to continue their protests against the disqualifications.