Kinda think this was part of the new Nafta.
Mexico agrees to Trump policy forcing migrants to wait in Mexico as asylum requests processed: report
https://thehill.com/homenews/administration/418077-mexico-agrees-to-trump-policy-forcing-migrants-to-wait-in-mexico-as
Mexico’s incoming administration has agreed to support a new policy from the Trump White House that would require migrants seeking asylum to remain in Mexico as their requests are processed, The Washington Post reported Saturday.
Mexican officials and senior members of president-elect Andrés Manuel López Obrador’s transition team told The Post that the incoming administration accepted the plan, called “Remain in Mexico,” in a sharp change to long-standing asylum rules that allowed migrants to file asylum claims after entering the U.S. either legally or illegally.