The abolition of the 10p introductory income tax rate is threatening Gordon Brown's authority as Labour MPs echo opposition criticism on the issue.
Mr Brown returns from his three-day trip to the US to criticism from ministerial aides, who are supposed to tow the line when it comes to government policy.
Mr Brown announced the abolition in his final Budget as chancellor in 2007 but it only came into effect, alongside a two-point cut in the basic income tax rate to 20 per cent, last weekend.
Yesterday both the Conservatives and Liberal Democrats spoke out against the policy, which they claim will make about five million people worse off.
'All of our customers are international and we need those transport links to be as efficient and effective as possible'
'Because key gateways have been capacity constrained, a lot of freighter services now terminate in mainland Europe'
Now four parliamentary private secretaries, the lowest ranking of government, have spoken out.
Stephen Pound, PPS to employment minister Stephen Timms, told ITV1's Evening News that the government had to "get out of this somehow".
Jeff Ennis, PPS to Cabinet Office minister Ed Miliband, admitted "everybody has concerns" about the situation while science minister Ian Pearson's PPS Celia Barlow has written to the prime minister about her "concerns" on the issue.
Finally, education minister Bill Rammell's aide Dave Anderson believes "we are doing the wrong thing".
Pressure is now growing on Mr Brown, who received disappointingly meagre coverage stateside because of the Pope's visit at the same time, to assert his authority over his own party.
He only has limited time to do so, however. Ex-minister Frank Field has tabled an amendment to the finance bill demanding compensation for those affected and MPs will vote on it next week.