Angry peers could summon David Cameron to give evidence before their constitution committee if he refuses to make the new leader of the Lords a full Cabinet member.
A source on the committee told Politics.co.uk the only reason the move was not made when it met on Wednesday morning was because the rationale behind the prime minister's decision was not confirmed.
Since then Cameron's preference for William Hague to remain a full Cabinet member over the new leader of the Lords, Tina Stowell, has become clear, prompting what backbenchers are now calling a "crisis" for the second chamber.
This is thought to be the first time the Lords has been without a representative in Cabinet since the Second World War. The situation, which followed Cameron's decision to maintain Hague's Cabinet status because of his 'first secretary of state' job title, is thought to be unprecedented in peacetime.
Members of the Lords feel their new leader will struggle to put across the House's view in Cabinet meetings because of her diminished status.
Feelings are running especially high among government backbenchers. Cameron now faces demands from Tory peers, who voiced their strong feelings forcefully at a meeting of the Association of Conservative Peers yesterday, to back down.
"The House is simply not going to accept what exists at the moment," one Tory peer told Politics.co.uk.
"There is only one way of bringing it to a satisfactory conclusion and end the damage... matters are clear and it now remains to be seen whether what was expressed so clearly in the House is noted and the appropriate rectifying action is taken in Downing Street."
Tina Stowell defended the PM's decision in the Lords yesterday. Photo: (c) Parliament
No 10 remains defiant over the issue, pointing out that Stowell will attend all Cabinet meetings.
And one government minister in the Lords dismissed the idea that Cameron might be forced to endure questioning from disgruntled peers over his reshuffle, pointing out that on previous occasions Lords select committees have struggled to persuade Cabinet ministers to give evidence.
Speaking in the Commons this morning, Hague told MPs: "When the Cabinet meets tomorrow, all those full members of the Cabinet, attending Cabinet, have exactly the same rights, they'll join in exactly the same discussion. It's not a distinction there needs to be a huge constitutional debate about."
Such an attempt by the constitution committee, which will meet again to discuss its options next Wednesday, would be a last-resort.
But many peers expect Cameron will back down before then as other interim measures are put in place to pressure Downing Street.
Rumours in the Lords last night were centring on the possibility of a cross-party motion being tabled for debate early next week.
Such a development would put Stowell in an extremely difficult position, as she defended the effective downgrading of her job in the Lords yesterday.
The new leader, facing hostile questions from peers on all sides of the House, said she expected to contribute to Cabinet in exactly the same way as her predecessor, Jonathan Hill, who will be Britain's next European commissioner.
"I am absolutely confident that the prime minister has given me the authority I need to represent your lordships in Cabinet," she told peers.
"I don't need status in order to get things done. I have got the authority I need and I will be judged on the work that I do."
Jan Royall, Labour's shadow leader of the House, said she was "deeply dismayed that the prime minister could treat this House with such contempt", however.
She and other peers voiced concerns about the status of the Lords rather than the politician in charge of it.
Jack Cunningham, a Labour peer, said "the prime minister has diminished the standing and rank of this House".
Roger Crickhowell suggested a possible answer for Cameron, who was forced to back Hague over Stowell because of a statutory limitation on the size of the Cabinet.
"The only limit arises on paid members of the Cabinet under the 1975 Act," he explained.
"Therefore, it ought to be possible to arrive at a solution that enables the Cabinet to be large enough to provide what the whole House thinks should happen: that the leader is a member of the Cabinet."
Stowell faced pressure from peers immediately after the debate, where she was seen talking with senior colleagues from across the Lords.
She is now expected to take the House's concerns to the prime minister. Labour sources indicated the opposition would press a cross-party motion to a vote if Cameron does not back down.