Labour is demanding that Welfare Reform Minister Lord Freud come to Parliament to explain his controversial suggestion that some disabled workers are "not worth" the minimum wage.
The Conservative peer has been allowed to remain in his job after apologising for the comment, which sparked furore among disability charities and was branded "offensive" by Deputy Prime Minister Nick Clegg.
But he has been withdrawn from scheduled frontbench duties in the House of Lords today, in a move which Labour said indicated that he does not enjoy the "full confidence" of Prime Minister David Cameron.
Shadow work and pensions secretary Rachel Reeves said it was "unacceptable" for Lord Freud to remain in his post.
In a letter to the PM, she demanded to know whether Mr Cameron had spoken to the peer before giving him "a clean bill of health", and whether any work had been done by Government departments on proposals to allow disabled people to be employed at below the £6.50-an-hour minimum wage.
Lord Freud was recorded at a fringe meeting of last month's Conservative Party conference responding to a Tory councillor who suggested that people with mental health problems may be unable to work because employers are unwilling to pay them the statutory minimum.
He replied: "You make a really good point about the disabled ... There is a group - and I know exactly who you mean - where actually, as you say, they're not worth the full wage and actually I'm going to go and think about that particular issue, whether there is something we can do nationally, and without distorting the whole thing, which actually if someone wants to work for £2 an hour, and it's working, can we actually..."
Mr Cameron flatly disowned the peer's remarks when ambushed by Labour leader Ed Miliband at Prime Minister's Questions and later ordered him to apologise amid opposition calls for his head.
In a statement last night, Lord Freud offered "a full and unreserved apology", adding: "I was foolish to accept the premise of the question. To be clear, all disabled people should be paid at least the minimum wage, without exception, and I accept that it is offensive to suggest anything else.
"I care passionately about disabled people. I am proud to have played a full part in a Government that is fully committed to helping disabled people overcome the many barriers they face in finding employment."
Mr Clegg said Lord Freud's comments had "cause huge offence", telling LBC radio: "I think what was so offensive to people ... was when he used this word 'worth' and he said some people with disabilities weren't worth the minimum wage. I think that is what has, quite rightly, touched a raw nerve because it's making a comment about someone's individual value."
The Deputy Prime Minister said the peer's comments were "deeply distressing and offensive to people".
But he added: "That shouldn't stop any of us having a discussion and, frankly, a difficult discussion - because some of these issues are difficult - to get more people with disabilities and with other disadvantages in life into the workplace."
Asked if it was wrong for people who wanted to work for £2 an hour to be allowed to do so, Mr Clegg said there were examples where it was accepted that people were paid below the usual level of the minimum wage.
"As a society, we say it's acceptable to pay apprentices a different kind of minimum wage. We have a minimum wage operating on a different scale depending on your age," he said.
In her letter to Mr Cameron, Ms Reeves said: " Lord Freud's remarks were completely unacceptable, and it is also unacceptable that someone with these views remains in charge of such an important post in your Government."
She called on ministers to release details of any work commissioned in the Department for Work and Pensions and other government departments relating to disabled workers' right to the minimum wage and demanded that Mr Cameron order Lord Freud to come to Parliament today to explain himself.
" If you cannot agree to this people will only conclude that your Government has something to hide, that you cannot publicly defend your position in relation to disabled people's entitlement to the minimum wage, and your inaction will haunt you," Ms Reeves told the PM.
"Charities yesterday said that Lord Freud's comments were offensive and shocking. Mencap said that he should 'reflect on his position'. It is unclear, however, how far a member of your Government would have to go in offending disabled people in order to lose their job, when in many other walks of life the comments by Lord Freud would have led to a resignation.
"You said in the House of Commons yesterday that Lord Freud's views are 'not the views of anyone in the Government', and yet his continued presence in the DWP suggests otherwise."
Downing Street made clear that Mr Cameron has not personally spoken with Lord Freud since the row broke.
Asked repeatedly at a regular Westminster media briefing whether the two men had spoken, a Number 10 spokeswoman said only that "the PM's office has made clear the PM's views" to Lord Freud.
Conservative backbencher Jackie Doyle-Price raised concerns about the impact of the minimum wage on disabled people's chances of finding work.
The Thurrock MP wrote on Twitter: "Anyone who denies that the minimum wage is a barrier to employment for the less able is living in cloud cuckoo land."
Responding to Ms Doyle-Price's comment, Labour spokeswoman for the disabled Kate Green said: "Yet another senior Tory has joined Lord Freud in attacking disabled people and disability charities, supporting his suggestion that some disabled people are worth less than the minimum wage.
"It is David Cameron who is living in cloud cuckoo land if he thinks Lord Freud should still be in his job.
"It is disgraceful that these views continue to go unchallenged in the Conservative Party. When is the Prime Minister going to take action?
"The mask is slipping from David Cameron's Conservatives. The nasty party is back."