Iran's main pro-democracy student group has called for a national boycott of next month's parliamentary elections.
Angry MPs are holding a sit-in against the ban in parliament
It said a mass ban of reformists from standing meant there was no chance of a free ballot, according to a statement carried by the state Irna news agency.
The Office to Consolidate Unity also urged reformist MPs to continue their protests against the poll blacklist.
Reformists oppose the conservative Guardians Council's ballot ban on more than 3,000 candidates.
"The reason why people are so disillusioned is because of the existence of powerful bodies which in the end render parliament powerless," the group said in its statement.
It said the only way out of the political deadlock is to hold a referendum on the future of the Islamic republic.
The BBC's correspondent in Tehran says up until now the student movement, historically a powerful political voice in Iran, has kept a low profile in this crisis.
In the past they have accused the reformists of failing to live up to their promises.
President Mohammad Khatami, himself a reformist, says he still believes the row can be resolved but warned he would not accept even a single "unfair" disqualification.
"Even if one person has been disqualified unfairly, as president, I will defend his right," Mr Khatami told reporters after a cabinet meeting on Wednesday.
The president said ministers and vice-presidents had submitted their resignations in protest over the mass disqualifications.
But with negotiations continuing, he said he "will not accept resignations of any kind".
The 12-member Guardians Council has disqualified more than a third of the 8,200 people - including more than 80 sitting MPs - who applied to run in the 20 February elections.
So far it has reinstated about 700 of the disqualified candidates, after Iran's supreme leader, Ayatollah Ali Khamenei, ordered a review.
It is still examining appeals and is due to announce its final decision on the others on 30 January.