A Delaware federal judge on Wednesday blocked the planned $367 million merger of market-leading radioactive waste disposal companies EnergySolutions Inc. and Waste Control Specialists, ruling in favor of government attorneys who argued the tie-up would violate U.S. antitrust law.

The decision, from U.S. District Judge Sue L. Robinson of the District of Delaware, was filed under seal at the request of the companies, which had asked that their confidential information be kept private. The parties have until June 28 to agree on a redacted version of the opinion to be made public.

The ruling followed a 10-day bench trial in May, where attorneys for the U.S. Department of Justice's Antitrust Division argued that the deal was presumptively illegal and would lead to higher prices and less innovation in markets that were already experiencing high levels of concentration.