By Frances Harrison
BBC News, Tehran
Registration of candidates standing for election to Iran's local councils and a key body called the Assembly of Experts is due to start.
Allies of President Ahmadinejad are hoping to win conrol
The assembly chooses Iran's supreme leader and can amend the constitution.
The 15 December polls will determine whether allies of ultra-conservative President Mahmoud Ahmadinejad gain control of these influential bodies.
Candidates still have to be approved by the watchdog Guardian Council, which inspects their Islamic credentials.
The main contest for the Assembly of Experts will probably be between supporters of the moderate former President, Hashemi Rafsanjani, and hardline cleric Ayatollah Taqi Mesbah-Yazdi.
Mr Rafsanjani has yet to confirm his candidacy but he looks likely to stand in order to try to curb the almost complete power of the ultra-conservatives. Ayatollah Mesbah-Yazdi is the ideological inspiration for President Ahmadinejad and is in charge of sending hundreds of Shia clerics abroad to spread Iran's revolutionary brand of Islam.
He is a shadowy and very powerful figure who does not give interviews to foreign journalists. Reformists accuse him of preaching that violence has a role in Islam.
Whoever has the most supporters in the Assembly of Experts will be in a position to choose the supreme leader when Ayatollah Khamanei dies or retires.
The supreme leader is the most powerful man in Iran with unquestioned authority over foreign policy and the future direction of the country.
But the local elections will also be important in gaining control over the grassroots level and building up local support bases before the next presidential elections in three years time.