Ayatollah Montazeri, a dissident grand ayatollah residing in holy Shia city of Qom, has issued a Fatwa saying the current Iranian regime is unjust and can be removed. Ayatollah Montazeri was one of the leaders of the Iranian revolution , but has been a dissident in recent years.
From The Middle East Research Center:
Query: "What is the ruling regarding holders of government positions, whom shari'a law requires to act justly, honestly, and wisely... if they [do not fulfill] these requirements to any degree, but behave in a manner diametrically opposed to them?"
Reply: "If none of the requirements mentioned in this query are met, this automatically, and without any need for impeachment, brings about the de facto collapse of the velayat [the 'jurisprudent,' meaning Iranian Supreme Leader Ali Khamenei] and of the government that is in charge of administering social affairs [i.e. the government of Iranian President Mahmoud Ahmadinejad] – and renders null and void all decrees issued by those who hold government positions...
"In the event of a breach of any article of the contract between the two sides – namely [the contract] between the position holder and the people, who appointed him – the people may remove the position holder from his post."