A consumer group sent a letter to the top senators on the Senate Judiciary subcommittee on Antitrust, Competition Policy and Consumer Rights on Monday, urging the lawmakers to probe Apple's agreements with e-book publishers.
The Consumer Federation of America said they believe Apple and the publishers are guilty of price-fixing, and antitrust regulators should take action against the companies.
The Justice Department is currently investigating the arrangements.
Although the Senate does not have the power to take action against individual companies engaging in anti-competitive conduct, the antitrust subcommittee often probes business deals and practices.
The Consumer Federation claimed that the agreements cost consumers more than $200 million per year, and that figure will "grow dramatically if the Department of Justice does not take action to stop this practice."
The Justice Department is reportedly close to a settlement with three e-book publishers, but the two remaining publishers and Apple are resisting the government's offer.