Major League Baseball has issued the Los Angeles Dodgers a serious warning after slugger Adrian Gonzalez gave pitcher Shohei Otani a signed jersey last fall, a source said Thursday.

Under the rules of the posting system, the MLB strictly prohibits its teams from directly or indirectly contacting players who have yet to reach free agency before obtaining permission to negotiate with them.

Gonzalez met Otani, who pitches for the Hokkaido Nippon Ham Fighters, on Nov. 10 when he was in Japan with the Mexico national team for an exhibition tour. The two spoke during batting practice, and Gonzalez gave Otani a Mexico jersey with his autograph and the message, “Looking forward to seeing you in the States,” as well as Dodger paraphernalia.

The MLB also warned its 30 teams not to make contact with Otani this spring, when the Fighters were holding camp in Peoria, Arizona, and notified theteam and Nippon Professional Baseball of the situation.