Liberal Democrats fighting the government's NHS reforms are demanding ministers back down over plans to make the health regulator promote competition.
The controversial health and social care bill places a statutory obligation on Monitor to encourage competition, to the frustration of senior Lib Dems.
politics.co.uk understands Nick Clegg has been presented with the party's latest demands, as the "pause" over the legislation continues.
At the top of the list is a requirement that Monitor should promote coordination and collaboration among health agencies, as well as competition.
John Pugh, co-chair of the party's backbench policy committee on health issues, is expecting a response from the leadership in the next two to three days.
"You have to give the regulator a dual mandate at the very least and expect it to promote cooperation and collaboration as the instrument of efficiency and patient benefit," he said.
"If you could do that, then you have a sensible body looking at the mandate. If you don't do that, you have an anarchic element within the NHS."
Shirley Williams, former MP Dr Evan Harris and MP Andrew George are among the prominent Lib Dems to have opposed the fundamental approach underpinning the health and social care bill.
Their concerns about the proposals for Monitor are echoed by health thinktanks and professional bodies, who fear an unfettered emphasis on competition will undermine standards in the NHS.
"There are very real concerns about where untrammelled competition will take us," Dr Pugh added.
"How much can a bill that was originally constructed with competition being the major theme be reconstructed without thinking you've got to construct another bill?
"You may reach a point where if you denature the existing bill to the extent that you amend it massively, you're left with a fairly untidy looking bit of legislation."
Ministers have already abandoned the principle of price competition during the bill's committee stage, in what was viewed as a major climbdown.
That has failed to satisfy politicians, health experts and campaigners, however, who continue to have concerns about health secretary Andrew Lansley's plans.
Prime minister David Cameron told MPs yesterday lunchtime that the 'pause' would result in "significant and substantial" changes.
Mr Lansley did not go as far in parliament earlier this week, only insisting there would be "substantive" alterations earlier this week in parliament.
The health secretary is forcing the NHS to find £20 billion in efficiencies over the course of the parliament - a requirement which has only served to deepen opposition to the reforms.
"The BMA remains committed to the founding principles of a National Health Service delivered in a cooperative and coordinated environment where patients are guaranteed the most clinically appropriate and cost-effective care," the BMA argued in a briefing paper issued ahead of Monday's opposition debate on NHS reform.
"A fully open market, which the bill currently promotes, will make this unachievable.
"The listening exercise offers the government an additional avenue to reflect on the criticisms that have been voiced about the bill and it must take hold of this valuable window of opportunity to ensure that the legislation achieves the best outcome for patients, healthcare professionals and the NHS."