The merger of pipeline companies Energy Transfer Equity LP and Williams Cos. Inc. has been approved with conditions, the U.S. Federal Trade Commission (FTC) said on June 9.

Energy Transfer's proposed acquisition of Williams has been in doubt for months, with Williams accusing Energy Transfer of actively trying to break the $20 billion deal. The two companies have sued each other.

The commission said it would approve the merger on condition that the companies agree to sell Williams' 50% stake in an interstate natural gas pipeline that serves Florida, particularly its electric power companies.

The antitrust approval was the last regulatory hurdle for the deal and Williams is committed to closing it as soon as possible, the company said.

A representative of Energy Transfer did not immediately respond to a request for comment.

The merger, announced last September, was intended to create more stability for both companies in the face of low oil prices.

The companies are set to face off in Delaware's chancery court on June 20 over tax issues that Energy Transfer said are hobbling the deal, as well as claims by each party that the other had broken their contact.

Williams shareholders are scheduled to vote on the deal on June 27. Under the current terms, the merger has to close by June 28 or the agreement expires.