CHICAGO (AP) — Major League Baseball has warned its teams against encouraging players to withdraw from high school baseball to avoid the amateur draft and pursue the increased flexibility of international free agency.

The memo was sent to front offices Monday by John D’Angelo, Major League Baseball’s vice president of amateur and medical baseball operations.

“It has come to our attention that Clubs have been encouraging amateur players in the United States to withdraw from, or otherwise refrain from playing, high school baseball in the United States and/or Canada, in order to try to establish residency in a foreign country, in an effort to make themselves eligible to sign under the International Amateur Talent System instead of the Rule 4 Draft,” the memo reads.

The memo calls the efforts “highly inappropriate,” and a violation of major league rules and the league’s collective bargaining agreement with its players. Clubs that engage in the practice are “subject to significant penalties,” which could include the loss of draft picks or international bonus pool money.