Nobel peace prizewinner Shirin Ebadi, a human rights lawyer, threw her moral weight behind their boycott of Friday's poll by saying she would not vote, to protest at the mass disqualification of reformist candidates by unelected clerics.
In a scathing six-page open letter, about 100 outgoing deputies accused the country's absolute Islamic leader of allowing his appointees to "violate the legitimate freedoms and rights of the people" in the name of Islam.
"Now the institutions under your supervision, after four years of humiliating the parliament and blocking its legislation, have blocked the fundamental right of the people to choose and be chosen."
The letter was handed to journalists at a protest meeting by more than 30 blacklisted MPs in parliament on Tuesday, but Iran's official media did not immediately report it.
The MPs challenged Khamenei, whose word is normally never questioned, to say whether he pulled the strings behind the mass exclusion of candidates, which plunged Iran into one of its most serious crises since the 1979 revolution.
"Do the members of the Guardian Council dare to resist your orders? Or is it that, as rumours say, despite your public statements, they were permitted by you to disqualify these people illegally and widely?"
Statement by blacklisted reformist MPs
"Do the members of the Guardian Council dare to resist your orders? Or is it that, as rumours say, despite your public statements, they were permitted by you to disqualify these people illegally and widely?" they asked.
The Guardian Council's 12 members are all appointed directly or indirectly by Khamenei. They have power to veto legislation and candidates on loosely defined Islamic and legal grounds.
In the past, reformists who have questioned the powers of the supreme leader, enshrined in a 1979 constitution that gave Ayat Allah Ruh Allah Khomeini and his successors the upper hand over elected bodies, have landed in prison.
Ebadi, whose award shone an uncomfortable spotlight on the struggle for human rights in the Islamic republic, told Reuters: "I will not vote myself because I don't know those who have been qualified. I'm not ready to vote for someone I don't know."
Ebadi is not ready to vote for
someone she does not know
"The first principle of democracy is that people should have the right to vote for anyone they want," she said.
Her comment ran counter to efforts by the authorities to mobilise a big turnout despite widespread public apathy and anger among reformists at the blanket ban on 2500 contenders.
Massive turnout urged
In a sermon last week, Khamenei called for a massive turnout to give the enemies of the Islamic system a slap in the face.
President Muhammad Khatami, a moderate reformist who failed to get the bans overturned, appealed to Iranians on Monday to cast their ballots despite "some unfairness" to prevent a hardline minority from seizing control of the country's future.
Reformist MPs staged a sit-in to
protest their disqualification
His own brother, Muhammad Reza, is among 80 protesting lawmakers barred from seeking re-election.
The main reformist group among Iran's two million students, the Office to Consolidate Unity, is also calling for a boycott.
The campaign manager of the main conservative coalition, the Alliance for the Advancement of Islamic Iran, voiced confidence the turnout would be up to the average in democratic states despite a largely invisible campaign with few well-known names.
Denouncing the excluded reformists as extremists who had failed to address people's real economic and social problems, Hussain Fadaii forecast at a news conference that 60%
would vote nationwide and 40% in Tehran.
Political scientists expect a much lower turnout, especially in the big cities that were the reformists' bastions.
If, as expected, the conservatives dominate parliament, it will make Khatami a weaker lame duck in his last 16 months in office and could threaten timid advances in press and cultural freedom, already under attack from the hardline judiciary.