In a request from the players’ union, the MLBPA, the players asked for "documents that would reflect interclub communications and communications between the commissioner's office and clubs about free-agent negotiations".
Baseball's labour contract prohibits teams from acting in concert in regard to free-agent players.
Many agents believe the union's inquiry is "absolutely appropriate".
"I think there's enough out there that makes it worth investigating, clearly," said one agent. "I've had several free agents that have gotten too many similar offers, virtually identical, not to suspect something.
"And I've heard it from other agents, too. One agent told me he had at least five identical offers for a client."
A players’ union official said the general unease stems from "a weird sense" that general managers, in conversing with agents, knew "a little too much" about what other clubs were doing.
It isn't the first time questions have been raised about collusion among owners.
The owners were found guilty of collusion after the 1985, 1986 and 1987 seasons. They paid $280m (EUR260m) in damages when the cases were settled in 1990.
Rob Manfred, management's top labour lawyer, denied the collusion allegations.
"Our view is that any suggestion that there was any improper activity in this market was ludicrous," Manfred told local media.
"The market was characterised by extensive competitive bidding for top free agents.
"Moreover, there are important external factors that one would have expected to have an impact on the market, including baseball's economics, the economy generally and the new agreement."
Legal issues will form a key part of the topics to be discussed at SportAccord, the leading industry conference taking place in Madrid between May 12-16.
To find out how YOU can attend, click on the link below to visit the official SportAccord website.
