The social enterprise the Wise Group is considering legal action against the Department for Work and Pensions after it decided to award the two Work Programme contracts in Scotland to private companies.
The Wise Group, which employs 650 staff, believes the DWP ignored its own guidance, which asked bidders to give voluntary organisations at least 30 per cent of work in the supply chain.
The Wise Group planned to do 45 per cent of the work itself, give 30 per cent to charities and 25 per cent to the private sector.
It believes its attempts to involve voluntary organisations might have made its bid too expensive.
"We have some misgivings about how the decision was reached and, as a result, we are taking legal advice," said a spokesman for the Wise Group.
"We estimate these contracts could have been worth as much as £150m over five years," he said.
She told Third Sector it was highly unusual for the government to deviate from its own criteria. "They have either changed it or ignored it," she said.
A DWP spokeswoman said giving 30 per cent of work to the voluntary sector, while an important part of the process, was never a specific contract requirement.
"We were also seeking input from local public sector organisations and small-to-medium-sized enterprises," she said. "Together, these organisations make up 30 to 40 per cent of both Working Links' and Ingueus's proposed supply chains.
"Their bids were also strongest across the board, offering good levels of service and good value for the taxpayer, and this is why they have been successful."