Delta and Aeromexico were set to offer more than 90 daily flights between the countries this year under a codeshare agreement that allows each carrier to sell seats on the other's flights, Delta said in October.

The U.S. Department of Transportation (DOT) announced in a written government order that the carriers would need time to wind down their agreement, setting a tentative Oct. 26 deadline.

The decision comes on the heels of decisions by the Mexican government affecting operations at the Mexico City International Airport (AICM), which the DOT said "called into question" the conditions needed for the Delta-Aeromexico tie-up, citing a lack of a fully-liberalized air transportation deal consistent with other U.S. government rules.

Also known as an "open skies agreement," the policy gives carriers more control over routes, capacity and pricing.

Last year, Mexican officials made sweeping changes to operations at AICM, the country's busiest airport, choosing to move cargo flights to a newer airport on the outskirts of town.

Later, slot availabilities for commercial flights were slashed, in another bid to reduce saturation at the crowded hub and move operations to the new Felipe Angeles International Airport, which has yet to see traffic kick off.

(Reporting by Kylie Madry; Editing by David Alire Garcia)