The UK decision to suspend some arms exports to Israel has bolstered the case for Congress to follow the example of its ally, US campaigners for a ban have said.

The campaigners are pressing the US Senate and the house to pass a joint resolution of disapproval blocking authorisation for an unprecedented $20bn (£15.2bn) weapons sale. The massive transfer was notified to Congress last month when it was in recess.

The US state department has said the UK decision to suspend arms sales has no bearing on US policy since the two countries have separate arms exports control regimes. The degree of private anger with the US over the UK decision is contested, but one UK Foreign Office source said it was comparable to the US anger when David Cameron as foreign secretary said Israel should not have veto power on recognising Palestinian statehood.

The Biden administration’s anger is likely to increase if the UK decision becomes a potent talking point in the domestic US debates on suspension of arms sales.

Annie Shiel, the US advocacy director at the Center for Civilians in Conflict, said both regimes were designed to implement international humanitarian law. “It is critical that the US considers the fact that one of its closest allies has found there is a clear risk that this equipment could be used to commit serious violations of international law,” she said.

“That risk speaks directly to US foreign policy since that policy prohibits the US from transferring arms when it finds ‘it is more likely than not’ that the arms could be used to commit serious violations of international law. That is the standard that the UK government clearly feels has been met, and that means that the US government is flagrantly ignoring the law.”

Amanda Klasing, the advocacy director of Amnesty International USA, said the tightly confined context in which Palestinians lived in Gaza meant the risk of a violation of proportionality and distinction central to humanitarian law was difficult to avoid. “It means there really is no question left for lawyers and that is where the UK lawyers have ended up,” she said.

Citing the use of 2,000lb bombs in densely populated areas, she said: “There are specific weapons in which there is just no feasible way to comply with international law. What the UK tells us, what the context tells us, is that at some point the lawyers are going to raise the real significant risks associated with the US continuing to transfer weapons.”

The campaigners hope the UK example will embolden more members of Congress to challenge the US policy. At minimum, they want to attract support from many of the 50 representatives who called for the supply of weapons to be curtailed if Israel went ahead with a major invasion of Rafah in southern Gaza.

In the Senate only one senator is required to put the issue to a vote, but the procedure is more complex in Congress. A vote would be required by the final full week of September. The pressure would be unwelcome to the Kamala Harris presidential campaign as it seeks to sidestep a divisive issue inside the Democrats.

The arms order includes $18.8bn worth of F-15 fighter jets, $774m of 120mm tank shells, medium-sized tactical vehicles totalling $583m, and $262m of joint direct attack munitions.

Josh Ruebner, the policy director at the US non-profit Institute for Middle East Understanding, said it was nonsensical to the point of “defying rational discussion” for the Biden administration “to urge Israel to accept a ceasefire and yet provide more weapons to commit this disgusting level of violence”.

He said polling by YouGov in the three swing states of Pennsylvania, Arizona and Georgia, commissioned by IMEU, broadly showed that if arms sales were banned, for every lost voter the Democrats would pick up seven extra votes.