US regulators have sued Amazon, alleging that the internet giant is illegally maintaining monopoly power.
The Federal Trade Commission (FTC) said Amazon uses "a set of interlocking anticompetitive and unfair strategies" to push up prices and stifle competition.
Amazon said the lawsuit was "wrong on the facts and law, and we look forward to making that case in court".
It is the latest technology giant to be sued by US regulators.