Four New Orleans tour guides claim their First Amendment rights are being trampled by city regulations requiring them to pass a history exam, submit to drug testing and undergo a criminal background check.

City officials claim they have a strong interest in regulating guides to protect the cash-cow industry of tourism. But Matthew Miller, an attorney for the guides, told FoxNews.com his clients - who give tours of the city's French Quarter, Garden District, cemeteries, restaurants, bars and other locations - practice a "constitutionally protected activity" no different from street performers or public preachers who talk about religion or politics.

"Speaking in the public forum is protected by the First Amendment," Miller said Thursday. "And the First Amendment protects your right to speak regardless of what you know."

New applicants must achieve a minimum score of 70 percent on a historical, cultural and sociological exam to become a licensed city tour guide, in addition to being at least 18 years of age and in possession of a driver's license.