Dozens of skilled jobs are at risk after it was confirmed that Wolverton company Railcare has been placed in administration.
Rail Union RMT has called for urgent intervention by Business Secretary Vince Cable to save the workers from redundancy.
The union claims Railcare asked the Government for help during a “short-term cash flow crisis”, but the request was turned down.
Earlier this week Railcare, which employs a total of 500 people in Milton Keynes and Glasgow, failed to pay its staff wages.
Earlier a planned takeover of Railcare by a German company had collapsed, as did crisis talks with another potential buyer.
A union spokesman said: “RMT understands that although Railcare has a full order book and plenty of work in the pipeline from the train operators via the fleet rail leasing companies, they ran into a cash flow problem which has forced the move into administration.”
This threatens the jobs at former British Rail plans in Glasgow and Milton Keynes, said the spokesman.
RMT blames the “franchising shambles“ of the West Coast “fiasco” for Railcare’s financial problems.
RMT General Secretary, Bob Crow, told the Citizen: “This crisis has left 500 staff unpaid and without any security.
“Vince Cable and the Government have a moral and economic duty to intervene urgently to save these jobs and protect the scheduled work,” he added.