A complaint challenging Equitable Resources' proposed acquisition of The Peoples Natural Gas Co. for $970 million has been approved by the Federal Trade Commission, the regulatory agency announced Thursday.

Peoples is a subsidiary of Dominion Resources Inc., and Equitable and Dominion Peoples are each other's sole competitors in the distribution of natural gas to nonresidential customers in certain areas of Allegheny County, including Pittsburgh, according to the FTC.

The complaint alleges that the proposed transaction would result in a monopoly for many customers who now enjoy competition. The deal includes the acquisition of Hope Gas Inc., another subsidiary of Dominion, but the complaint does not challenge the Hope part of the deal.

Equitable's proposed acquisition of Dominion Peoples must be approved by the Public Utilities Commission, which is expected to announce its decision later this month or in early April, according to the commission.

The FTC has not yet filed for a preliminary injunction in federal court to block the deal pending trial. However, the commission voted 4-to-1 to issue the administrative complaint and to authorize a preliminary injunction, if it becomes necessary, the FTC stated in a prepared release.

In a prepared statement, Thomas Farrell, Dominion's president and CEO, said the PUC was the proper agency to consider the merits of the deal, not the FTC.

A PUC administrative law judge recently recommended approval of the acquisition, saying greater efficiencies and reduced gas costs to consumers were among the benefits, Farrell said in the statement. Dominion planned to challenge the FTC decision, he said.