Unions are calling for urgent reassurances over the jobs, pay and pensions of thousands of workers following the "disastrous" news that Carillion has gone into administration.
Yorkshire workers await news as Carillion collapses into liquidation after crunch talks fail
Officials from several unions representing workers on the railways, construction sites, prisons, hospitals and schools are seeking information from the company and ministers.
Rail, Maritime and Transport union General Secretary Mick Cash said: "This is disastrous news for the workforce and disastrous news for transport and public services in Britain.
"We have been warning since Thursday night that we thought the collapse of the company was imminent.
"The blame for this lies squarely with the Government who are obsessed with out-sourcing key works to these high risk, private enterprises.
"RMT will be demanding urgent meetings with Network Rail and the train companies today with the objective of protecting our members jobs and pensions.
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"The infrastructure and support works must be immediately taken in house with the workforce protected.
"Transport Secretary Chris Grayling and his Tory colleagues must be forced to take responsibility for this crisis which is wholly of their making."
Jim Kennedy, Unite's national officer for local government, said a public inquiry was now needed.
"Public services, vast amounts of public money, thousands of jobs - including in a lengthy supply chain of insecure agency workers who are also at risk - and workers' hard-saved pensions are all in danger of being dragged under by yet another bout of reckless corporate irresponsibility.
"There are also serious questions that need to be asked and answered about Carillion's conduct.
"Did directors move to protect their bonuses before the financial stability of the company?
"Has the company mushroomed because it built its business on unrealistic undercutting and blacklisting?
"Why did the government continue to hand over public money to a company that had issued repeated profits warnings?"
Rehana Azam, national officer of the GMB union, said: "The fact such a massive government contractor like Carillion has been allowed to go into administration shows the complete failure of a system that has put our public services in the grip of shady profit-making contractors.
"The priority now for the Government and administrators is making sure kids in schools still get fed to day - and our members still have jobs and pensions.
"There is no place for private companies who answer to shareholders, not patients, parents and service users in our public services.
"What's happening with Carillion yet again shows the perils of allowing privatisation to run rampant in our schools, our hospitals and our prisons."