The Federal Trade Commission has sued the bargain chain Dollar General for what it characterized as "long-running deceptive pricing practices" by charging customers more once they reach the register than the prices that are displayed on shelves and in advertisements.

Twenty states joined in the complaint, filed by the U.S. District Court for the Middle District of Tennessee.

It said that Dollar General failed to correct the issue despite what it said was "extensive corporate knowledge of the problem." "Dollar General has betrayed the trust of millions of American consumers and imposed significant financial harm on communities and consumers who are already struggling to make their paychecks last," wrote Christopher Mufarrige, director of the FTC's Bureau of Consumer Protection.