]Amazon.com has decided to stop telling third-party sellers on its platform that they cannot offer lower prices on competing websites, a source said on Monday.

The source gave no details on the decision.

The decision comes in the wake of a letter from Sen. Richard Blumenthal (D-Conn.), arguing that the practice would "stifle market competition and artificially inflate prices." The Dec. 19 letter was sent to Federal Trade Commission Chairman Joseph Simons and Assistant Attorney General Makan Delrahim.

Blumenthal said Amazon had enforced its policy in the past by threatening to remove merchants who violated the contract clause. He argued the policy raised antitrust concerns and should be investigated by U.S. regulators.

Germany's antitrust authority launched an investigation into whether Amazon is exploiting its market dominance in its relations with third-party retailers in November.

Germany is Amazon's second-biggest market.