The U.S. Federal Trade Commission warned 20 dog waste bag manufacturers and marketers to revise or remove their promotional materials when it found that their claims of sustainability amounted to deceptive advertising.

The agency sent letters to the unnamed bag makers pointing out that labeling their products “biodegradable” or “compostable” are unqualified statements, leading consumers to believe that the bags degrade like grass clippings or leaves in natural settings, yard compost piles or trash disposal streamed to landfills.

Plastic doesn’t break down within a year, if at all, in landfills, and very few recycling facilities accept this waste, according to the FTC’s guidelines. “Therefore, compostable claims for these products are generally untrue.”

“Consumers looking to buy environmentally friendly products should not have to guess whether the claims made are accurate,” said Jessica Rich, Director of the FTC’s Bureau of Consumer Protection.