Two of the most senior Democrats in the US Senate have thrown their weight behind a bill to impose new sanctions on Iran, a move the White House believes could sabotage delicate negotiations over a final nuclear deal.

Democrat Robert Menendez, who chairs the powerful foreign affairs committee, is the lead author of the bill, alongside Chuck Schumer, the third-ranking Democrat in the chamber, and a Republican senator, Mark Kirk.

According to a copy of the draft obtained by Foreign Policy magazine, it would permit Barack Obama to suspend the implementation of harsh new sanctions on Iran for the duration of the nuclear talks, but only on the basis of strict criteria laid down by Congress.

The administration would need to certify to Congress every 30 days that Tehran was meeting a set of conditions, including those laid out in a temporary accord reached in Geneva last month. The bill also compels the Obama administration to provide Congress with a detailed progress report on negotiations at monthly intervals.

Iranian experts are increasingly concerned that Congress poses one of the greatest obstacles to a final nuclear settlement with Tehran.

Technical experts are fine-tuning how the temporary deal reached in Geneva last month will be implemented, but it is expected to come into force sometime in January. It would initially last six months, but officials close to the negotiations say it would almost certainly have to be renewed.

The deal provides limited sanctions relief to Iran – which, according to US estimates, will provide a $7bn boost to Iran's economy. In return, Iran has agreed to freeze its nuclear program, destroy stockpiles of higher-grade uranium and commit to more rigorous inspections.

Forged between Iran and a six-nation group comprising the US, three European countries, Russia and China, the temporary deal was intended to provide momentum – and space – for more sustained negotiations in search of a final, comprehensive agreement.

Crucially, it contains a clause in which the US administration committed itself to “refrain from imposing new nuclear-related sanctions”, although the wording provided some acknowledgement that President Obama could not control legislation passed by Congress.

However, a high-ranking official closely involved with the negotiations, who spoke anonymously because they were not authorised to talk publicly about nuclear talks, told the Guardian a new sanctions bill would be seen by the Iranians to be in breach of “the spirit” of the agreement. The official said a new bill would risk Iranians walking from the negotiating table before the Geneva agreement has even begun, adding: “We could be back to square one.”

The temporary Geneva deal has been received with widespread scepticism in Congress, not least because it paves the way to Iran maintaining some capacity to develop civil nuclear fuel on its territory, albeit under strict limitations. Washington’s hardliners insist Iran should not be permitted any nuclear enrichment capability, arguing they should be forced to dismantle all their reactors and instead import nuclear fuel from abroad. The Menendez-Schumer bill comes close to making this demand.

It would prohibit Obama from waiving sanctions on Iran unless, under a final agreement, the country dismantles “illicit nuclear infrastructure, including enrichment and reprocessing capabilities and facilities and the heavy water reactor and production plant at Arak”. It also contains a provision enabling Congress to override any easing of sanctions authorised by the White House bypassing a "joint resolution of disapproval" against any final deal.

It is unlikely to be debated before the recess but will likely resurface in early January. The White House has so far managed to dissuade Democrats on Capitol Hill from pursuing bills and resolutions they argue would imperil the current talks, but it is unclear how much sway the administration has over Menendez and Schumer. Harry Reid, the Democratic majority leader in the Senate, is also likely to play a crucial role in determining whether an Iran sanctions bill reaches the floor.

Last week the Democratic chair of the Senate banking committee, Tim Johnson, shelved a similar Iran sanctions bill, which passed overwhelmingly by the House in July, after pressure from the White House.

The administration also appeared to have convinced the House Democratic whip Steny Hoyer from supporting a resolution that called for additional sanctions on Iran and laid out a tough set of criteria that should be met before any final deal. Hoyer was closely involved in drafting the resolution, and only pulled his support at the very last minute.