May 23 (Bloomberg) -- U.S. Senator Herb Kohl, chairman of the Senate antitrust subcommittee, urged regulators to block the proposed combination of XM Satellite Holdings Inc. and Sirius Satellite Radio Inc., saying the merger will hurt consumers.

Sirius's proposed $4 billion purchase of XM would violate antitrust law and harm consumers, Kohl, a Democrat from Wisconsin, wrote today in a letter addressed to the Justice Department and the Federal Communications Commission.

The combination of the two pay radio services ``would cause substantial harm to competition and consumers, would be contrary to antitrust law and not in the public interest, and therefore should be blocked by your agencies,'' Kohl wrote.

The Justice Department is in the early stages of a review, said Blair Levin, a Washington-based analyst with Stifel Nicolaus & Co. The review will include ``a lot of economic analysis that was not the subject of congressional hearings,'' he said.

Shares of Washington-based XM, the largest pay-radio service, rose 46 cents to $11.52 at 4 p.m. New York time in Nasdaq Stock Market trading. They have fallen 20 percent this year. New York-based Sirius rose 6 cents to $2.86.

Congress has no authority to approve or reject the transaction. Kohl's Subcommittee on Antitrust, Competition Policy and Consumer Rights held a hearing on the combination in April and recently wrapped its inquiry in to the deal.

To contact the reporter on this story: Christopher Stern in Washington at cstern3@bloomberg.net

Last Updated: May 23, 2007 16:26 EDT