The Federal Trade Commission warned six manufacturers of cars, video game consoles and mobile devices that their overly strict warranty-voiding tactics aren’t going to fly anymore.

In a Wednesday letter to six unnamed companies, the agency determined that the use of “warranty seals” — stickers that are placed on internal components, over screws for example, and which must be broken in order to repair or open a device — are illegal.

The FTC also said that companies cannot void warranties if consumers choose to repair their products with third-party parts — a policy that hurts “consumers who pay more for them as well as the small businesses who offer competing products and services,” said Thomas B. Pahl, acting director of the FTC’s Bureau of Consumer Protection.

The verbiage used in the FTC’s letter matched the wording used by Hyundai, Sony and Nintendo in their warranties.

The FTC gave examples of “questionable provisions,” one of which matches the wording used by Hyundai, requiring customers to use company parts, while another used by Sony for its Playstation 4 gaming console voided warranties if a warranty seal was “altered, defaced, or removed.”

The FTC cited the 1975 Magnuson-Moss Warranty Act in its warning, which states that companies cannot make such statements “unless warrantors provide the parts or services for free or receive a waiver from the FTC.”

The companies in question have been given 30 days to revise their promotional and warranty materials.