WASHINGTON (Reuters) - Senators Amy Klobuchar, Elizabeth Warren and other Democratic lawmakers expressed “serious concerns” on Monday about T-Mobile US, Inc’s (DTEGn.DE) plan to buy rival Sprint Corp (S.N), focusing on the planned deal’s effect on lower-cost wireless plans, Klobuchar’s office said in a press statement.

FILE PHOTO: A smartphones with Sprint logo are seen in front of a screen projection of T-mobile logo, in this picture illustration taken April 30, 2018. REUTERS/Dado Ruvic/Illustration/File Photo

In a letter sent to the Justice Department’s antitrust chief, Makan Delrahim, and Federal Communications Commission Chairman Ajit Pai, the senators said that they worried that the deal between the No. 3 and No. 4 wireless service providers would lead to higher prices for consumers.

FILE PHOTO: The Sprint logo is displayed on a a screen on the floor of the New York Stock Exchange (NYSE) in New York City, U.S., April 30, 2018. REUTERS/Brendan McDermid/File Photo

“T-Mobile and Sprint have led the way in offering wireless products and service options that are more appealing to lower-income consumers, including no contract plans, prepaid and no credit check plans, and unlimited text, voice, and data plans,” the lawmakers wrote.

While AT&T and Verizon dominate the U.S. wireless market overall, T-Mobile is the most popular among customers who make less than $75,000 per year, and Sprint’s prepaid brand Boost counts 83 percent of its users in that income range, according to data from Kagan, S&P Global Market Intelligence data.

T-Mobile has 38 percent of the U.S. prepaid market, while Sprint has 16 percent, which would give the combined company 54 percent, according to S&P.

In addition to Klobuchar and Warren, the letter was signed by Democratic Senators Richard Blumenthal, Mazie Hirono, Tina Smith, Tom Udall and Ed Markey,

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