Bob DuPuy resigned Tuesday as Major League Baseball's chief operating officer following 8½ years as commissioner Bud Selig's top aide.

The move is effective Oct. 31, and Selig doesn't currently intend to replace him.

DuPuy was Selig's outside lawyer when he became executive vice president for administration in 1998. He was promoted to president in March 2002 and replaced Paul Beeston.

Relations between Selig and DuPuy have become strained in recent years. DuPuy declined to comment on his situation this week.

Earlier Tuesday, Gene Orza said he will retire as the players' association No. 2 official on March 31. The 64-year-old has been with the union since 1985.

DuPuy first attracted attention in baseball when he negotiated the $280 million collusion settlement with the union in 1989 after arbitrators found owners violated their labor contract by acting in concert to not sign free agents after the 1985, 1986 and 1987 seasons.

An attorney with Foley and Lardner in Milwaukee, he was Selig's primary lawyer from 1992-98 after the Brewers owner helped lead a revolt that led to commissioner Fay Vincent's resignation.

He was one of management's primary negotiators, along with executive vice president Rob Manfred, of the 2002 and 2006 collective bargaining agreements, and was a driving force behind the formation of Major League Baseball Advanced Media, baseball's Internet division.

DuPuy, who moved from Milwaukee to New York to work for Selig, will assist MLB in special projects including the Oakland Athletics' quest for a new ballpark.