The Office for Fair Trading (OFT) has accused 112 construction companies of bid rigging and cover pricing.
It issued a Statement of Objections against the firms, some of which, it believes have worked together to inflate prices.
John Fingleton, OFT chief executive, said: "Cartel activity of the type alleged today harms the economy by distorting competition and keeping prices artificially high."
Investigations started in 2004 after it received a complaint, which led it to believe there was evidence of further violations.
OFT carried out site visits at 57 firms and says it has evidence of further cover pricing activity in "thousands of tender processes" which it is yet to focus on.
Mr Fingleton hopes the investigation will "send out a strong message to the construction industry about the seriousness with which we view suspected anti-competitive behaviour".
"Businesses have no excuses for not knowing and abiding by the law."