Mexico is in talks with its U.S. counterparts on whether to allow U.S. federal air marshals to use Taser stun guns on commercial cross-border flights with U.S. airlines. Talks to allow U.S. federal marshals in Mexico have been going on for years, but nothing has yet been finalized, Reuters reports.

In a meeting on January 18 in Mexico’s foreign ministry, officials from both countries agreed to “study the convenience of negotiating an agreement for the deployment of Federal Air Marshals on commercial flights,” according to an official Mexican document seen by Reuters.

In a statement on January 29, Mexico’s foreign ministry confirmed that the government was evaluating the plan’s potential operational and security benefits. Adding that no agreement has yet been reached.

On January 30, Mexico’s National Security Commissioner Renato Sales said in an interview that they and the U.S. were looking into an agreement that could allow armed U.S. federal air marshals to travel on commercial cross-border flights.

“They would only be on commercial (U.S.) flights, on (U.S) airlines, not on Mexican airlines,” Sales said in the interview. He also noted that the U.S. federal air marshals would carry stun guns, not lethal weapons, and that they would be undercover.

Many further details have not yet been disclosed. It is still not clear if the air marshals would travel on U.S.-bound flights, Mexico-bound flights, or both.

U.S. Federal Air Marshal Service spokesman Thomas Kelly declined to comment on the proposed agreement, but clarified that air marshals are “armed federal law enforcement officers” whose mission is “in-flight protection of U.S.-flagged aircraft, crew members and passengers.”

Although Mexico is attempting to deepen security ties with its neighbor, the use of weapons by foreigners is sensitive and tightly regulated, and negotiations on allowing U.S. officials to carry guns could prove to be difficult.

Nevertheless, it is a clear sign of a shift in policy, Mexico News Daily writes. Since the 9/11 terrorist attacks, Mexico has agreed to place its own security agents on certain flights, but never allowed armed U.S. officials onboard its commercial airlines.

Mexico has been trying to improve cooperation with its top trade partner on security, immigration, and foreign policy ever since President Donald Trump took office. What is at stake here is the possibility for Mexico to renegotiate the North American Free Trade Agreement (NAFTA) in the most favorable terms ahead of a July 2018 general election, Reuters reports.