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.

ESPN was the first to report on the warning. The memo was obtained by the AP on Tuesday.

An amateur draft was established for residents of the United States and Canada in 1965 and extended to residents of U.S. territories such as Puerto Rico in 1990. Competitive balance selections are the only picks from the 20-round draft that can be traded, and there are penalties for teams that exceed their allotment for signing bonuses.

There is more freedom for players and teams under the international amateur talent system. There are penalties for teams that exceed their international bonus pool money, but players can choose their new homes.

Major League Baseball has pushed for an international draft, but the idea has been spurned by the players’ association.