The NFL’s throwback uniform wave has hit celebrated new heights this season with retro designs from teams such as the Philadelphia Eagles, Seattle Seahawks, and Tampa Bay Buccaneers winning widespread praise from fans and pundits.

Now, a new legal fight involves one of the most revered looks of all.

The league has sent a formal cease-and-desist letter to the University of Houston, according to documents obtained by the Houston Chronicle, asking them to immediately stop their “blatant copying” of the Houston Oilers’ former uniforms. In addition to preventing any merchandise sales, the NFL also sought to discontinue any social media or promotional efforts involving the uniforms.