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.