Liga MX teams could relent on their scouting efforts in the United States after the Mexico Football Federation (FMF) have warned them about possible rule violations. The Mexican clubs could face the same sanctions that Barcelona faced back in April of 2014 for breaking Article 19 of FIFA's Regulations on the Status and Transfer of Players.
According to Article 19, players under the age of 18 are prohibited from international transfers unless special circumstances are in play. You can find a list of those, which includes if the parents of the player move to the country in which the new club is located for reasons not linked to football, right here.