The U.S. Food and Drug Administration on Thursday will tell a federal judge in Kentucky that ordering the agency to delay enforcing new tobacco laws will have "devastating consequences" on public health.

The FDA is facing a challenge to its new tobacco powers, signed into law in June, from tobacco companies including Camel cigarette maker Reynolds American Inc. (RAI) and Commonwealth Brands Inc. The companies say the law imposes unprecedented restrictions on their First Amendment rights and want a federal court in Bowling Green, Ky., to order a preliminary injunction to stop enforcement of certain provisions in the regulations.

A judge for the District Court for the Western District of Kentucky is holding a hearing on the preliminary injunction request and could soon decide whether to grant the injunction.

The law restricts tobacco companies from using color in most ads, bars them from saying certain products are less risky than others and stops them from selling tobacco products in combination with other items, such as soda and mouthwash.

"It is crucial to the public health that tobacco products not be marketed as reduced-risk products unless they will, in fact, reduce risks," the FDA said in a brief filed with the court.

The injunction request relates only to the restrictions on marketing tobacco products with other consumer items, and restrictions against advertising that a tobacco product is less risky than other tobacco product. Restrictions on color in ads don't go into effect until June 2010.

The companies want to be able to make claims in ads and on boxes that certain tobacco products contain smaller amounts of harmful ingredients, such as being low in tar, and are, therefore, less risky than other tobacco products.

This issue is important to companies that make smokeless tobacco products. Reynolds, for instance, makes Camel Snus, a type of tobacco that comes in a pouch in flavors like "frost" and "mellow."

In their briefing documents, the companies argue that such information is truthful and should be given to consumers.

The FDA says such information gives consumers the "mistaken belief" that the products are safe to use. The agency will allow companies to make such claims only after they prove the product does reduce a consumers risk for tobacco-related diseases. That appears to be a high hurdle. The agency notes that medical devices and prescription drugs must go through a rigorous review process before they can be sold to treat or reduce the risk of disease.

The companies say they aren't completely against the FDA authority to regulate tobacco, and that they support restrictions in marketing and advertising to children.

While Lorillard Inc. (LO) is a party to the overall lawsuit challenging the advertising restrictions imposed by the law, it isn't a party to the preliminary injunction, according to a company spokesman. The company says it didn't join the request for injunction because it doesn't intend to market tobacco products with claims that they are less risky than other tobacco products.

-By Jared A. Favole, Dow Jones Newswires; 202.862.9207; jared.favole@dowjones.com

(Alicia Mundy contributed to this report.)