The coalition is planning on "packing the House" with Conservative and Lib Dem peers to increase their majority in the Lords, Labour has claimed.
Baroness Royall, Labour's leader in the House of Lords, accused the government of attempting to "swamp the opposition" with new appointments.
“Beating your opponents in the Lords by argument is one thing, and one thing the government have often been unsuccessful in doing. But beating your opponents by unfairly boosting the strength of your own side is a very different thing indeed, and in
effect amounts to political gerrymandering of the worst kind," she said.
In a speech to the Centre for Opposition Studies, the peer said there was "scope as an opposition to effect change, real change" but the composition of the Lords "heavily favours" the government.
"Looked at among the political votes alone, excluding the crossbenchers, bishops and others, the coalition has 56.4 per cent of the votes, against Labour’s 43.6 per cent – a political majority currently of 70 for the coalition."
Despite the coalition's political majority, the government has suffered several defeats in the Lords - including on the controversial NHS and welfare reforms.
Royall says that this has led to "muttering" that "this kind of behaviour would be replied to by bringing in extra peers to boost the government’s voting strengths."
“A new list is certainly on the way, and the Westminster rumour mill has it at a further 60 new peers – 40 more for the Conservatives, 15 for the Liberal Democrats and five for Labour," she said.
Royall acknowledged the final number could be smaller, but said: “Having loaded the dice, the coalition is now intent on creating a completely stacked deck. The purpose, though, is not solely to swamp the Opposition, so severely limiting the constitutional role of the House of Lords to scrutinise and revise legislation, though it certainly does do that."
Ahead of the speech the Labour peer warned that Lords reform would severely inhibit the government's legislative programme.
"If or when such a bill arrives in the Lords, little or nothing else will get done, quite frankly," Royall told the Guardian.
She said: "The thought that this government could put House of Lords reform at the centre of its programme for the next parliamentary session I find quite astonishing.
"If it does, it will say a lot to the people of the country about this government's priorities."