The Iranian parliament has passed the first stage of a bill which would force the government to resume its uranium enrichment programme.
Iran denies claims it wants to build nuclear weapons
It received the endorsement of all 247 MPs present, the speaker said.
The international community has asked Iran to suspend all uranium enrichment, or face referral the United Nations Security Council.
Iran agreed in October last year to suspend the programme, but has since resumed the manufacture of centrifuges.
Centrifuges refine uranium, which can then be used in nuclear weapons.
Iran insists the uranium would be used only for generation of electricity.
Earlier, a Foreign Ministry spokesman said the government would be obliged to abide by whatever legislation Parliament endorsed.
Speaking after the vote, the Speaker, Gholam Ali Haddad Adel, said the message to the outside world was that Iran would not give in to international pressure.
"The message of the absolute vote for the Iranian nation is that the parliament supports national interests," he said, the Associated Press news agency reported.
During the three-hour debate, some parliamentarians argued against the bill, saying it was not necessary to have new legislation because Iran's rights were already guaranteed in the Nuclear Non-Proliferation Treaty.
Others said a new law would strengthen the hands of Iran's negotiators.
Iranian officials are due to meet their European counterparts on Friday in Paris for a third round of talks on a package of proposals to allay international concerns about Iran's nuclear programme.
The EU nations are offering Iran civil nuclear technology if it agrees to abandon uranium enrichment.
Western diplomats say there needs to be a clear response to the proposals by mid-November, or Europe will back US efforts to refer Iran to the UN Security Council.