Midnight meant lights out on lighting up in New Orleans bars and casinos.

Ninety days after Mayor Mitch Landrieu signed the “Smoke-Free Air Act” into law, it now is illegal to smoke in the city’s bars and casinos, with the exception of existing cigar and hookah bars. “Vaping” also is still allowed at existing e-cigarette retailers.

It already was illegal to smoke in restaurants.

The ban has been hailed by supporters as an important step in protecting bartenders and other service workers, plus performers at music clubs, from the effects of secondhand smoke and as a move to bring New Orleans in line with other major cities that prohibit smoking indoors in public spaces.

But critics say the new law infringes on the freedom of bar owners and customers and could cause significant revenue losses.

Harrah’s Casino and dozens of French Quarter bars and restaurants filed a suit last week in Civil District Court seeking to strike down the ban. A hearing on the suit is set for May 21. The companies failed to persuade a judge to issue a temporary restraining order that would have prevented the city from enforcing the ban in the meantime.

The casino company also is trying to get state legislators to put pressure on the city to drop the ban, saying that having to provide an entirely smoke-free environment could cost the casino 20 percent of its business and cost the state treasury millions of dollars.

The city still is working out the details of how it will enforce the ban. For now, business owners are charged with telling their patrons about the law and ensuring that they comply.

The city also has set up a website, nola.gov/smokefree, to accept complaints about noncompliant businesses. Complaints also can be made to the city’s 311 phone service.