The U.S. Federal Trade Commission said on Monday it had sued 1-800 Contacts, which it called the largest U.S. online retailer of contact lenses, alleging the company illegally maintained anti-competitive agreements with rival online contact lens sellers.

These agreements “suppress competition in certain online search advertising auctions and … restrict truthful and non-misleading internet advertising to consumers, resulting in some consumers paying higher retail prices for contact lenses,” the federal regulator said in a statement.