Iran's parliament has threatened to pull out of the nuclear Non-Proliferation Treaty if Western pressure over its programme increases.
Tehran says the West is trying to bully it into action
The threat came in a statement made a day before key UN members discuss a tough draft resolution on the issue.
Pulling out of the NPT is the ultimate threat of non-cooperation by Iran, says our Tehran correspondent.
A withdrawal would mean the country's programme could no longer be inspected by the UN nuclear watchdog, the IAEA.
The MPs' statement, which the Iranian news agency said had the support of 160 of 290 members of parliament, was addressed to UN Secretary General Kofi Annan.
It said that unless the row was resolved peacefully, parliament would "have no choice but to call on the government to retract its signature of the Additional Protocol and to place on its agenda an examination of Article 10 of the NPT [Non-Proliferation Treaty]".
The Additional Protocol allows snap inspections of nuclear facilities, while Article 10 covers the procedure for leaving the treaty.
The threat was echoed by President Mahmoud Ahmadinejad, who said the Non-Proliferation Treaty had no validity if it threatened the rights of a nation.
Western nations are concerned Iran is seeking a nuclear weapons capability, though Iran denies this.
The draft UN Security Council resolution threatens further steps if Iran does not stop uranium enrichment.
But the draft - which was introduced by Britain and France - has been criticised by Russia and China, who oppose the fact the resolution is to be legally binding and could lead to sanctions or even military action if Iran does not comply.
Iran says it is within its international rights to seek nuclear power and suspending its nuclear programme is not on the agenda.
Though both the West and Iran say they want a diplomatic solution to this crisis, the hostile rhetoric is intensifying and there is no sign of negotiations to defuse the mounting tension, says our Tehran correspondent Frances Harrison.
A withdrawal from the NPT - which requires a three-months' notice - would mean the outside world would have no idea what is going on inside Iranian nuclear sites.
And it could be a precursor to starting a weapons programme, though Tehran strenuously denies that it wants a nuclear bomb, says our correspondent.
Foreign ministers from the five permanent members of the Security Council and Germany are meeting in New York on Monday to discuss the issue.
It will also be the first major engagement for the UK's new Foreign Secretary, Margaret Beckett.
On Saturday, the US Ambassador to the UN, John Bolton - who wants tough action against Iran - said he would be willing to discuss another way of making the resolution compulsory, but added that he had not heard any new ideas yet.