The future of the House of Lords would be called into question if ministers press ahead with plans to curtail its powers, the Lord Speaker has said.
Baroness D'Souza said the Lords "should be free to scrutinise, to question and to hold the government to account".
A review of the Lords was launched after it blocked government plans to cut tax credits in October, to the anger of Conservative ministers.
But Baroness D'Souza said limiting it would "question what it is there for".
During the last parliamentary session, the Lords inflicted 60 defeats on the government, including several changes to the housing bill last week.
In return ministers have been clear they are looking into ways of making that harder.
The review, conducted by Lord Strathclyde, recommended taking away the absolute veto the House of Lords has over laws, called statutory instruments, and instead create a new procedure allowing them to send secondary legislation back to the House of Commons to "think again".
They would only be allowed to do this once, enabling the House of Commons to have the final say and push through its agenda even if the Lords disagrees.
'Free to scrutinise'
Baroness D'Souza, who is standing down from the role of speaker in the summer, told the BBC's Sunday Politics: "Obviously we would expect the Lords to want to retain their power to scrutinise... if you start curtailing or eroding or limiting the power of the Lords to do its job, there is a question as to what it is there for."
She said the Lords "should be free to scrutinise and to question and to hold the government to account and to send back legislation it feels is not adequate, either in terms of its clarity or because it infringes the individual liberties we all hold dear".
"There's going to be lively debate about this in the House of Lords and I think there will be a lot of views expressed."
She added that she would also be pushing for a motion on the issue of reducing the size of the Lords saying it should not be larger than the House of Commons, and suggesting the number of peers be cut to around 500 from its current 807.
Baroness D'Souza said she believed at least 20% of peers in the house should be independents or cross-benchers and no one party should have a political majority, adding these changes could be implemented by 2020.
The current size of the House was so large, it was starting to have an impact on the ability of the House of Lords to hold the government to account, the Lord Speaker added.
Sunday Politics will be broadcast on BBC One at 11:00 BST.
