Leaders of the Senate Judiciary Committee’s Subcommittee on Antitrust, Competition Policy, and Consumer Rights Dec. 19 asked the Federal Trade Commission to investigate allegations that Google unlawfully favors its own products over competitors when displaying search results.

The letter’s authors, Sens. Herb Kohl (D-Wis.) and Michael S. Lee (R-Utah), chairman and ranking member respectively of the subcommittee, took no position on the legality of Google’s practices under the antitrust laws and the FTC Act. Kohl and Lee wrote that they believed that the Google competitors’ complaints warranted serious scrutiny by the agency.

The letter follows the subcommittee’s September hearing on...