Nick Clegg has accused critics of the government's work experience scheme of having "messed-up" priorities, ahead of a meeting between firms and employment minister Chris Grayling.
The scheme has been labelled "slave labour" for allegedly forcing some unemployed people to work or have their benefits withdrawn. However ministers insist the scheme is not mandatory.
The deputy prime minister said on Wednesday that critics of the programme should "think hard about what they are saying" before talking down a scheme that helps people get jobs.
"They are criticising a programme that is deliberately trying to help young people into work. I cannot for the life of me understand the kind of messed-up sense of priorities of people who want to prevent young people from finding opportunities to get into permanent work," he said.
Clegg said it was good to get unemployed people "off the sofa", adding: "All the evidence shows that on this scheme already, about 50% of youngsters get off benefits within a matter of weeks."
It comes as a group opposed to the scheme, Boycott Workfare, have planned action across the country on Saturday.
Spokesperson Steve O'Brien told The Huffington Post UK that it was Nick Clegg who needed to "think hard" about what he was saying:
"Boycott Workfare believe that the evidence shows that it is this government that have got a messed up sense of priorities by pushing a scheme which hinders economic recovery," he said.
"All the international research conducted on workfare shows that these schemes fail and that they do not deliver values for taxpayers' money.
"Boycott Workfare believe that Nick Clegg needs to think hard about a practical policy that guarantees people jobs. These schemes mean people work for up to six months for no pay and that does not make sense in the current economic climate."
It comes as the main union for staff in jobcentres and benefits, the Public and Commercial Services Union (PCS), announced it backed the anti-workfare campaign. PCS general secretary Mark Serwotka said campaigns had exposed the "true nature" of schemes that were "providing a pool of free labour for big businesses that could afford to pay proper wages.
"Instead of exploiting our young people and seeking to blame them for mass unemployment, the government should be helping to create long-term paid jobs and training to get people off benefits and into meaningful work," he added.
Several businesses, such as Poundland, TK Maxx and Waterstones have withdrawn from the programme.
Last week Tesco called on the government to stop making youths undertake work experience in exchange for receiving benefits.
Protests over the scheme at a Tesco store in FebruarySuggest a correction