Ex-deputy Labour leader John Prescott has called Labour colleagues John Hutton and Frank Field "collaborators".
His comments came after Mr Hutton agreed to review public sector pensions and Mr Field agreed to review poverty for the Conservative-Lib Dem coalition.
Writing on his blog he said: "I've been in politics for over 50 years but even I can't believe what's happening."
"They've made themselves human shields for the most savage and heartless Tory policies in 20 years," he added.
Mr Prescott adds in his blog he was "surprised to see Lib Dems used by the Thatcherites like Cameron and Osborne to provide cover in the Treasury for their heartless programme of cuts".
He said: "Watch them being used again as apologists for that VAT rise on Tuesday. But that pales into insignificance now Labour ministers have decided to collaborate with the Tories."
Including Labour MP Kate Hoey's role as adviser to London's Conservative mayor Boris Johnson, he said another thing the three "had in common" was that they "all tried to stop Gordon Brown becoming leader so perhaps we shouldn't be surprised they're happy to join a Tory-led coalition".
He said they were "human shields" for "policies that will hit the poorest and most vulnerable the hardest - the very people Labour was founded to protect. I would ask if they can live with their conscience but I'd question whether they even had one to begin with."
Mr Hutton's appointment to head the public sector pensions review was announced by Chancellor George Osborne, who said the former Labour defence secretary would bring a "clear and unbiased" analysis to the subject.
Mr Hutton said: "I am determined that this work should be conducted openly and transparently and that our conclusions will be underpinned with a comprehensive analysis and evidence-base."
Shadow chancellor Alistair Darling said he had spoken to Mr Hutton on Sunday and said his former cabinet colleague would want to make sure the review was "fully independent".
Mr Field, the MP for Birkenhead, said, after accepting the invitation earlier this month to review anti-poverty measures for David Cameron's government, that it was "a real opportunity to influence the next stage in how our counter-poverty strategy develops".
Ms Hoey said she was seeking "to make a difference" to people living across London in her role as an unpaid commissioner for sport for London's Conservative mayor, seeking to promote the best possible grassroots legacy from the 2012 Olympics.