It is the first poll since the 2009 presidential elections, which the opposition says were rigged in favour of President Mahmoud Ahmadinejad.
|Friday's election will be fought by a |
number of rival conservative groups
It is a contest between his supporters and hard-liners close to supreme leader Ayatollah Ali Khamenei.
The opposition Green Movement is not taking part. Its leaders have been placed under house arrest.
The authorities are urging voters to come out in large numbers, with some posters in the capital Tehran even warning that a low turnout might encourage foreign powers to launch military strikes.
But correspondents say even some of President Ahmadinejad's supporters are quietly calling for a boycott.
Mr Ahmadinejad has fallen out with Mr Khamenei in recent months, and some of his supporters complain that their candidates have been barred from standing.
The respective strength of the different conservative camps after this poll will define the balance of power for what may be a much more important vote - the 2013 presidential election, says BBC Iran correspondent James Reynolds.
However the results of the elections are unlikely to change Iran's stance on its controversial nuclear programme, he adds.
International sanctions imposed over Iran's nuclear programme have been having an effect on the economy.