May 28 (Reuters) - Scott Sheffield, the former CEO of

Pioneer Natural Resources, has requested the US Federal Trade

Commission to vacate its order that barred his inclusion on

Exxon Mobil's ( XOM ) board.

Sheffield also sought the dismissal of the proceeding

without further action, according to a comment filed by his

legal counsel before the regulator on Tuesday.

The U.S. antitrust regulator had given its go-ahead to

Exxon's $60 billion purchase of Pioneer earlier in May, but

barred Sheffield from Exxon's board on allegations that he

attempted to collude with the Organization of the Petroleum

Exporting Countries (OPEC) to raise oil prices.

"In straining to find a reason to criticize the merger of

Exxon and Pioneer, the FTC stepped well beyond its proper

mandate and unjustly smeared Sheffield," according to the

counsel's comment.

FTC did not immediately respond to a Reuters request for

comment.