A peer leading threats to block cuts to tax credits unless the government eases the impact on low-paid families has complained of being subjected to "unspeakable" bullying by George Osborne.
The Chancellor is under mounting pressure to mitigate the effect of the policy, with opposition parties and rebel Tory MPs threatening defeats in the Lords and Commons next week.
Threats to throw out the £4.4 billion cuts sparked warnings from David Cameron that peers should obey the convention that the House of Lords does not block financial policies approved by MPs.
The Prime Minister pointedly failed to rule out appointing hundreds of new Conservative peers to give the party a majority in the second chamber.
Crossbencher Baroness Meacher complained at the way she and others were treated over proposed "fatal" amendments that would kill off the policy.
"There has been enormous pressure coming from the Treasury, the Chancellor of the Exchequer, upon peers," she told BBC Radio 4's Week in Westminster.
"The weight on me has been unspeakable really. I think it's bullying tactics."
Threats included that he would "close the House of Lords, that he will create 100 new Conservative peers", she told the programme.
Mr Osborne insisted this week he was "comfortable" with the policy despite analysis by the independent Institute for Fiscal Studies (IFS) that the introduction of a higher minimum wage will not offset poor households' immediate losses.
The IFS calculates that millions of people will lose up to £1,300 a year from the Budget changes.
But with the Lords set to make its opposition known - perhaps via a Church of England bishops' motion decrying the failure to take into account the short-term impact - and senior Tory MPs leading a rebellion in a vote in the Commons later in the week, there are reports concessions may be made.