Iran's parliament has backed plans to begin uranium enrichment and end snap inspections by the United Nations if it is referred to the UN Security Council.
Iran's uranium plant at Isfahan is at the centre of debate
The UN nuclear watchdog is due to decide whether to refer Tehran over its secretive nuclear programme.
In a vote, 183 out of 197 Iranian MPs backed the proposals.
The US says Iran is developing nuclear weapons, denied by Tehran, and aims to prevent it enriching uranium - a key stage in producing weapons-grade fuel.
The session of Iran's parliament, the Majlis, was held just four days before the International Atomic Energy Agency is due to decide on referral to the Security Council.
Iranian state radio broadcast the entire session live.
The legislation must now be approved by Iran's ruling Guardian Council. Correspondents says that is likely on Tuesday, two days before the IAEA meets in Vienna.
IRAN'S NUCLEAR STANDOFF
September 2002: Work begins on Iran's first nuclear reactor at Bushehr
December 2002: Satellite photographs reveal nuclear sites at Arak and Natanz. Iran agrees to an IAEA inspection
September 2003: IAEA gives Iran weeks to prove it is not pursuing atomic weapons
November 2003: Iran suspends uranium enrichment and allows tougher inspections; IAEA says no proof of any weapons programme
June 2004: IAEA rebukes Iran for not fully co-operating with nuclear inquiry
November 2004: Iran suspends uranium enrichment as part of deal with EU
August 2005: Iran rejects EU proposals and resumes work at Isfahan nuclear plant
The decision echoes threats made by Ali Larijani, Iran's senior nuclear negotiator, who has promised a defiant response if Iran is referred to the Security Council.
The Security Council could impose economic sanctions on Iran.
The Majlis decision converts diplomatic statements into legislation that the Iranian government will be compelled to follow.
Iran's government "will be required to cancel all voluntary measures it has taken and implement all scientific, research and executive programs to enable the rights of the nation under the Nuclear Non-Proliferation Treaty," one MP quoted the bill as saying.
As a signatory to the Non-Proliferation Treaty, Iran insists that it has legal rights to pursue a civilian nuclear energy programme, including uranium enrichment.
However, Tehran concealed its nuclear activities from the outside world until they were revealed in 2002, prompting international suspicion.
Iran resumed uranium conversion, an earlier stage in the nuclear fuel cycle, at its plant in Isfahan when negotiations with the European Union broke down in August.
NUCLEAR FUEL CYCLE
Mined uranium ore is purified and reconstituted into solid form known as yellowcake
Yellowcake is converted into a gas by heating it to about 64C (147F)
Gas is fed through centrifuges, where its isotopes separate and process is repeated until uranium is enriched
Low-level enriched uranium is used for nuclear fuel
Highly enriched uranium can be used in nuclear weapons
In September the IAEA's board called on Iran to cease all nuclear fuel work, and threatened to refer Tehran to the Security Council.
An interim report last week revealed that Iran had information on how to build a key part of an atomic weapon from the network of disgraced Pakistani nuclear scientist AQ Khan.
Iran insisted it neither requested the information nor used it.
The disclosure heightened concerns among some IAEA members that over Iran's processing activities.
Tehran announced last week that it had begun processing a new batch of uranium, which can be used in a weapon in a highly enriched form.
The country's nuclear negotiators have regularly said they want to re-start enrichment, but have so far held back from unilateral moves.