Troubled construction giant Carillion's partners on the HS2 project have been forced to give assurances that they can step in to deliver on the work if required.
Carillion suffered a dramatic collapse in its share price last week after announcing a profit warning which saw almost £600 million wiped from its value.
But on Monday it was awarded a major contract to build part of the high-speed railway in partnership with Eiffage and Kier.
HS2 Ltd said in a statement that it "carried out additional due diligence" and the three companies have "confirmed that they underwrite the performance of each other in delivering the contract".
It added: "HS2, of course, will continue to monitor the situation."
Contracts worth £6.6 billion in total were announced by the Department for Transport (DfT) on Monday.
They will see tunnels, embankments and viaducts constructed between London and Birmingham.
A number of foreign firms were successful in bidding for the work, including Swedish-based Skanska, French company Bouygues Travaux and Austria's Strabag.
The contracts are estimated to support 16,000 jobs.
The final route of the Manchester and Leeds arms of the railway will be confirmed later.
Ministers suggested in November last year that the line should serve the existing Sheffield city centre station, after proposals to run trains to the Meadowhall shopping centre were shelved.
But critics have warned this will mean homes on the new Shimmer housing estate in nearby Mexborough being bulldozed.
Some residents found out about the HS2 plans just weeks after moving into the development of two and three-storey town houses.
High-speed trains are expected to begin operating between London and Birmingham in 2026.
Transport Secretary Chris Grayling said: "This is a hugely important step in the construction of Britain's new railway and underlines this Government's determination to deliver an economy that works for all.
"HS2 will deliver vital links between some of our country's biggest cities, helping to drive economic growth and productivity in the North and Midlands.
"As well as providing desperately needed new seats and better connecting our major cities, HS2 will help re-balance our economy.
"We will now get on with building the railway, while continuing to ensure affected communities get appropriate support and are treated with fairness, compassion and respect."
Opponents of the £55.7 billion project claim it will run over budget, create havoc during construction and have disastrous environmental consequences.
In February, Parliament granted powers to build the first phase of the line, which will see trains travel at high speed between London and Birmingham before running on from Birmingham on the existing West Coast Main Line.
Preparatory work has begun and major construction projects are due to launch in 2018/19.
Mr Grayling will soon publish a Bill to deliver Phase 2a from the West Midlands to Crewe, with services expected to begin in 2027.
Phase 2b from Crewe to Manchester, and Birmingham to the East Midlands and Leeds, is due to open in 2033.