The United States and Mexico are investigating if U.S. federal air marshals could be placed on commercial cross-border flights, a new report says.

Shortly after the Sept. 11, 2011, attacks on the U.S., Mexico said it would put Mexican security agents on various flights. However, U.S. officials were barred from boarding Mexico’s commercial flights.

Both the U.S. and Mexico have decided to “study the convenience of negotiating an agreement for the deployment of Federal Air Marshals on commercial flights,” a Mexican document says, according to Reuters. The issue was discussed on Jan. 18 at a meeting in Mexico’s foreign ministry.

U.S. sharp-shooters are put on domestic and international commercial flights entering and leaving the U.S. This is authorized by the Department of Homeland Security.

It’s uncertain whether U.S. air marshals would be placed on flights only entering the U.S., only entering Mexico, or both, a Mexican official said, according to the report. Additionally, it’s not certain if the air marshals would be permitted on U.S.-owned airlines or also on Mexican-owned airlines.

Additionally, the document claims that the U.S. and Mexico are negotiating ways to address “transnational criminal organizations” as each country plans to launch a bilateral investigative body to examine international criminal groups.

Under the Trump administration, the U.S. and Mexico have claimed Mexico has sought to improve cooperation with the U.S. on issues such as security, immigration, and foreign policy.

The report comes amid negotiations between the U.S., Mexico, and Canada concerning the North American Trade Agreement.