The construction giant Carillion has gone into liquidation this morning.
The company is a contractor for the planned HS2 railway line through Buckinghamshire, the East West line and the electrification of the Midland Mainline north of Bedford.
The firm - which employs 20,000 people in the UK - has debts of £1.5bn.
The Cabinet Office minister and MP for Aylesbury, David Lidington, said the government will do all it can to protect the company's workers.
"The first priority, and the one that I've asked all ministers and all officials to concentrate on is actually ensuring that public services continue," he said.
"So the message to workers is come into work today, there's important work to be done.
"As we go forward, some services will be taken in-house [and] some services will go out to alternative contractors in a manged, orderly fashion."