The three blocs include the Unified Iraqi list, headed by Iyad Allawi, Iraq's former prime minister, and two Sunni Arab groups that together competed for 92 of the parliament's 275 seats in the elections on 15 December.
Hasan Zaidan al-Lihaibi, a representative of the Sunni-dominated Iraqi Front for National Dialogue, said: "We will resort to peaceful options, including protests, civil disobedience and a boycott of the political process until our demands are met."
Al-Lihaibi told reporters in neighbouring Jordan that the decision followed four days of private meetings by representatives of the 100 parties that made up the blocs to draw up a "plan of action for revoking the elections' results".
Partial results from the election have shown that the United Iraqi Alliance, a religious Shia coalition, has a large lead.
Those results have been attacked by Sunni Arab and secular Shia parties, which claim that the election was tainted by fraud and other irregularities.
Abd al-Aziz al-Hakim's party
denies election fraud
The alliance, headed by Abd al-Aziz al-Hakim, a cleric, denies that there was any fraud and is urging Iraqis to accept the results as it tries to form a "national unity" government drawing people from all communities.
Al-Lihaibi said representatives from the three opposition blocs, which also include the Iraqi Accordance Front, a Sunni coalition led by Adnan al-Dulaimi, would meet Amr Moussa the Arab League's secretary-general this week to seek help.
Al-Dulaimi said: "We seek a new election under international supervision, with the government's militias far from the process."
Al-Dulaimi wants international
He said the Independent Electoral Commission of Iraq should also be distant from the process.
Al-Lihaibi, from the northern Sunni-dominated city of Mosul, said that his group was gathering "fraud evidence" to present them to the Arab League and the United Nations.
He said there was evidence pointing to Iranian "meddling in the election process" in Iraq. He said that some ballot boxes with forged votes had crossed from mostly Shia Iran.
He said: "Those who are leading the country now are implementing an Iranian agenda."