The main reformist party in Iran has said it may boycott the country's general election if too many of its members are barred from standing.
By Jim Muir
BBC Tehran correspondent
The registration of candidates began on Saturday, but leaders of the Participation Front fear their candidates could be vetoed.
The unelected Guardian Council has previously disqualified candidates without explanation.
Widespread public disillusionment could result in a low turnout on 20 February.
The current parliament, or maglis, is dominated by reformists who have won all major national elections since 1997, but they have been able to achieve little in office because of obstruction by entrenched hardliners.
Mohammad Reza Khatami leads the reformist Participation Front
A poor turnout could result in a victory by default for the conservatives.
One of the pieces of legislation that the reformists tried to push through would have changed the way the election procedures work.
They wanted to curb the role of the Guardian Council, a highly conservative unelected body. But the bill was vetoed by that very same council, so the first hurdle for all of the would-be candidates is still a rigorous vetting by the council.
The first question hanging over this election is therefore how many of the reformist candidates will survive.
Hopefuls have a week to register and their eligibility should be decided within the following 10 days.
The Participation Front, the biggest of the reformist factions which currently dominate parliament, has said it will take part in the race, but it reserves the right to pull out if too many of its entrants are disqualified.
At present much of the betting is that the reformists will do poorly at the polls even if their candidates get that far.
They have got little to show in practical terms for their years in office, largely because their efforts to bring about change have been blocked by an entrenched hardline minority.
Many of the millions of Iranians who voted overwhelmingly for the reformists are now bitterly disillusioned. Some have said they will not bother to vote.
That is what happened in city council elections last February where the turnout in Tehran was less than 12% and the conservatives won by default.
But other considerations come into play in a national election. There are no foregone conclusions in Iranian politics.