The Justice Department, in what it described as its strongest enforcement of an antitrust agreement in 20 years, said Thursday that it and Live Nation Entertainment have agreed to amend and extend the regulatory decree that allowed the giant concert company to merge with Ticketmaster nearly a decade ago.

Justice officials said the settlement came after the department found that Live Nation had repeatedly violated the existing agreement. Its investigation focused on complaints from competitors that Live Nation had used its control over the concert touring business to pressure music venues into signing contracts with its Ticketmaster subsidiary.

Such behavior, the Justice officials said, violated the terms of the consent decree that the government imposed as a condition of the merger in 2010 — a deal that created a colossus in the live entertainment business and has long been criticized for giving the company too much power.

Under a proposed amended agreement that the government filed in federal court in Washington, the decree, set to expire in July, would be extended to the end of 2025. Live Nation would also reimburse the Justice Department for its costs in enforcing the regulations, but would not be fined.