Companies in each of the French-owned groups are in the final stages of bidding separately for the £ 300 million overhead power line package.
Four bidders are in pursuit, including Colas Rail, owned by Bouygues, Rapide JV, a consortium of SPL Powerlines UK / INEO, owned by Equans, and Keltbray, Balfour Beatty, and China Railway Electrification Engineering Group Co.
The Competition and Markets Authority said it recognized that there were enough credible competitors for any future contract for the installation and maintenance of high-speed catenary systems in the UK.
But because the current HS2 bidding was at an advanced stage, merging companies could make the rest of the bidding process less competitive.
Colin Raftery, CMA’s senior director, said: “Competitive bidding helps ensure that taxpayers get the best deal possible when major public works, such as HS2, are carried out.
“The HS2 tender for overhead catenary systems is at an advanced stage, but the other bidders continue to compete in the final aspects of the contract.
“It’s important to make sure this process doesn’t get undermined, as this could lead to unnecessary additional costs and ultimately worsen taxpayers.
Companies have five business days to submit proposals to address CMA’s competition issues to address an in-depth Phase 2 investigation.