ST. LOUIS — As Michael Weiner prepares to take over from Donald Fehr as head of the players’ association, several agents are pushing the union to file a collusion grievance against teams over their behavior during the free-agent market last winter.

‘‘There’s a general level of suspicion in the air,’’ said Jeff Borris, an agent whose clients include Barry Bonds, Brian Fuentes and Jason Isringhausen.

The decision on whether to go ahead with a grievance will be one of the first major decisions for the union since Fehr announced his pending retirement last month and its executive board recommended Weiner, the union’s general counsel, for the top job.

‘‘The investigation is ongoing but not complete because of things to review,’’ Weiner said Monday before the All-Star Home Run Derby. ‘‘We’ve had some discussions with the commissioner’s office. I’ll know more I think by the end of the month.’’

Halfway through the season, agents also are worried about collusion because no major players eligible for free agency have agreed to contract extensions.

‘‘There are too many things that need to be explained,’’ said Seth Levinson, who represented nearly a dozen free agents following the 2008 season. ‘‘In my experience, there are no coincidences in a monopoly.’’

Weiner, who will take over from Fehr between the end of this season and the start of the 2010 schedule, struck a more cautious note.

‘‘The new market will be what it’s going to be,’’ he said.

The union filed collusion grievances following the 1985, 1986 and 1987 seasons. After arbitrators ruled in the union’s favor, management agreed to a $280 million settlement.

A triple-damages provision was inserted into the sport’s labor contract in 1990. As part of the latest collective bargaining agreement in 2006, players and owners settled potential claims that management may have conspired against free agents following the 2002 and 2003 seasons. The settlement, made with no admission of guilt, called for a lump-sum $12 million payment from money already earmarked for players to settle unfiled claims of collusive activity along with other pending grievances.

Some agents have said the union should have been more aggressive and more public in pursuing those claims.

Rob Manfred, Major League Baseball’s executive vice president of labor relations, said no improper conduct occurred.

‘‘The free-agent market proceeded in a manner that was completely consistent with the requirements of the basic agreement,’’ he said.