WASHINGTON — The next great First Amendment battleground is just six inches high. It is a license plate bearing the Confederate flag.

Nine states let drivers choose specialty license plates featuring the flag and honoring the Sons of Confederate Veterans, which says it seeks to celebrate Southern heritage. But Texas refused to allow the group’s plates, saying the flag was offensive.

On Monday, the Supreme Court will hear a challenge to that decision in Walker v. Sons of Confederate Veterans, No. 14-144, a case that considers the limits of free expression and the meaning of a charged symbol that many associate with secession and slavery.

Texas has hundreds of specialty plates. Many are for college alumni, sports fans and service organizations, but others send messages like “Choose Life,” “God Bless Texas” and “Fight Terrorism.”