In a statement, the company confirmed it was stepping back from its £170m contract to develop the second phase of the infrastructure scheme.
CH2M blamed its exit on "protracted delays and ongoing speculation". However, it has been reported rival firm Mace has raised concerns over the contract's award, as HS2's new Chief Executive, Mark Thurston, is a former employee of CH2M.
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In addition, the company's Managing Director, Roy Hill, was also seconded to HS2 as interim chief executive last October.
A spokesperson for CH2M said: "H2M today provided formal notice to HS2 Ltd that we are withdrawing our interest in the HS2 Phase 2b contract.
"CH2M has demonstrated all appropriate measures taken throughout to ensure the integrity of the procurement process. Notwithstanding these efforts, we have taken the decision to alleviate any further delays to this critical national infrastructure project which could ultimately lead to increasing costs to UK taxpayers, as well as to our firm.
"CH2M's reputation reflects excellence earned by placing the interests of our clients and communities first, best exemplified by our delivery of vital programmes like Crossrail, the London 2012 Olympics, the most sustainable to-date; HS2 Phase 1; and the Thames Tideway and Lee Tunnels."
(LM/CD)
