BBC regional analyst
Reformist leaders have described the move to bar them from next month's parliamentary elections as a coup d'etat.
The power struggle in Iran looks set to continue
They have promised to use all the means available to them to resist it, including sit-ins and boycott of the elections.
The Guardian Council normally disqualifies some hopefuls during elections in Iran. But reformists say this is the biggest disqualification of candidates in the country's parliamentary history.
More than 80 current MPs, including two deputy speakers and six heads of key parliamentary commissions, are reportedly deemed unsuitable by the hardline body to stand again for elections.
Most of them were outspoken critics of the country's human rights record.
Among those disqualified are deputies who recently wrote an open letter to the country's supreme leader, Ayatollah Ali Khamenei, urging him to take heed of the people's demands for more freedom and democracy.
It appears that the widespread barring of reformist hopefuls from the February elections is designed to rid the next parliament of the so-called undesirable elements.
But it is unlikely that the reformists leave the political scene without a fight. Their biggest problem, however, is probably the current general apathy among the Iranian people.
Most voters are deeply disappointed that the reformists have not been able to introduce more freedoms and improve the human rights situation in Iran.
If the Guardian Council does not back down in the next few weeks, the power struggle will intensify in the Islamic Republic
Therefore, the man in the street is unlikely to put his life in danger by yet again supporting the reformists and taking action against this decision.
The conservatives were aware of this public mood when they decided to disqualify their rivals from elections.
Had they expected a more vigorous public uproar, they would probably have taken a more moderate decision.
It appears that this large-scale disqualification of candidates will result in a low turn-out in the February general elections.
In that case it is highly possible that the conservative candidates will dominate the next parliament.
'Pressure on Khamenei'
But if the Iranian election is seen as unjust it will have damaging impact on the country's relations with the outside world, especially the European Union.
The legitimacy of the country's government will come under more internal and international scrutiny.
In the meantime, it is likely that the reformists will put more pressure on the country's supreme leader, Ayatollah Khamenei, to reverse the situation.
Because the key members of the Guardian Council are appointed by the ayatollah, the reformists will see him ultimately responsible for its actions.
If the Guardian Council does not back down in the next few weeks, the power struggle will intensify in the Islamic Republic.