Justice Department, FCC, and T-Mobile, U.S. Cellular face scrutiny from Warren.

• A group of six senators are urging the Justice Department and the Federal Communications Commission to examine a proposed agreement between T-Mobile and U.S. Cellular that would grant T-Mobile access to a portion of U.S. Cellular's wireless spectrum.
• Lawmakers propose that consumers may face higher costs if higher-priced carriers are allowed to charge more while lower-priced carriers merge.
• The Justice Department is being urged by lawmakers to reconsider the merger of T-Mobile and Sprint.

A group of Democratic senators are raising concerns about the proposal to acquire most of US Cellular and are urging the Justice Department and the Federal Communications Commission to closely examine and potentially challenge the deal.

The $4.4 billion deal announced in May 2024 would enable T-Mobile to utilize part of U.S. Cellular's wireless spectrum to enhance its coverage in rural areas and gain access to four million new customers. In a letter, six Democrats expressed their opposition to the plan, stating that it would increase costs for customers and restrict options.

The letter, obtained exclusively by CNBC, stated that additional consolidation in the market would have significant consequences, including reducing consumer options, intensifying the concentration of wireless spectrum ownership, and potentially resulting in higher prices and other negative impacts for consumers nationwide.

The letter was signed by Sens. Elizabeth Warren (Mass.), Amy Klobuchar (Minn.), Chris Murphy (Conn.), Bernie Sanders (Vt.), Cory Booker (D-N.J.), and Richard Blumenthal (Conn.).

Under the agreement, T-Mobile would lease space on U.S. Cellular's wireless spectrum and towers, retaining 70% of its own.

Previously, Warren and Klobuchar have expressed worries about T-Mobile's acquisitions and merger with Sprint.

In their Monday letter, lawmakers requested the Justice Department to reconsider the merger, stating that it resulted in billions of dollars in losses for customers of competing wireless carriers.

The letter stated that the merger resulted in the removal of a low-cost carrier from the market, thereby decreasing the competitive pressure on the remaining national wireless carriers to lower their prices.

According to a statement released at the time of the deal, a spokesman for U.S. Cellular stated that the partnership with T-Mobile would offer more competitive choices for UScellular customers, as they would benefit from T-Mobile's greater resources and ability to provide lower prices, more robust plans, and a better network experience.

A T-Mobile spokesperson did not immediately respond to a CNBC request for comment on the letter.