Kenner Mayor E. 'Ben' Zahn III speaks during an inaugural ceremony at the Pontchartrain Center in Kenner, La. Friday, June 29, 2018.

The ACLU of Louisiana on Wednesday condemned Kenner Mayor Ben Zahn's anti-Nike purchase policy for booster clubs as "unconstitutional," saying it violates the First Amendment and calling on him to rescind it immediately.

The policy is "based solely on the mayor's opposition to NIke's political expression," said a statement released on the group's website. It violates First Amendment protections against "content and viewpoint discrimination," the statement says.

"He is trying to stop booster clubs from symbolically expressing their support for political views the mayor detests. That’s a textbook First Amendment violation," the statement says. "Mayor Zahn, rescind your unconstitutional policy. Just do it," the statement concludes.

Zahn instituted a policy last week forbidding booster clubs affiliated with Kenner's recreation department from buying Nike apparel and requiring that all booster club purchases be approved by the city's recreation director. The policy prompted a backlash that drew attention nationally and protests locally.

Nike had just chosen former NFL quarterback Colin Kaepernick as the spokesman for its new "Just Do It" campaign. The ad highlighted the fact that Kaepernick's commitment to protesting police brutality and racial injustice by kneeling during the National Anthem is widely believed to have cost him his job in the NFL.

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That protest, which got a significant boost in visibility last season from critical statements by President Donald Trump, has sparked a backlash among those who feel that refusing to stand for the anthem is disrespectful to the military and those who serve.

Zahn defended his policy on Monday, saying he is simply trying to prevent taxpayer dollars from funding what he called a political agenda. 

On Monday evening, hundreds gathered at the Susan Park Gymnasium to protest, including local activists, politicians and members of the New Orleans Saints.