WASHINGTON, Jan 5 (Reuters) - Two groups representing auto dealers said on Friday they had filed a legal challenge to the Federal Trade Commission's new sweeping consumer protection regulations finalized last month.

The FTC said the new rules effective July 30 will ban bait-and-switch advertising tactics, prohibit charging for add-on costs that do not benefit consumers and require dealers to make key disclosures to consumers.

The National Automobile Dealers Association and Texas Automobile Dealers Association asked the Fifth Circuit Court of Appeals to block the new rule saying it is "arbitrary, capricious (and) an abuse of discretion." (Reporting by David Shepardson Editing by Chris Reese)