A group of senators is urging regulators to closely scrutinize the proposed merger between T-Mobile and Sprint, arguing that the deal could hurt wireless consumers.

Sen. Amy Klobuchar (D-Minn.) led a group of six Democrats along with Sen. Bernie Sanders (I-Vt.), in a letter to the Justice Department's Antitrust Division and the Federal Communications Commission (FCC), warning of the potential dangers of the $26 billion deal.

"As more than three-quarters of American adults now own smartphones, including many who depend on these devices for their primary connection to the internet, an anticompetitive acquisition in the wireless market could result in higher prices for American consumers or force some people to forego their internet connection altogether," the senators wrote.

The letter - addressed to FCC Chairman Ajit Pai and Makan Delrahim, the assistant attorney general for antitrust - notes how their predecessors had previously warned against the deal, which would reduce the number of national wireless service providers from four to three.

Critics say that shrinking the market would reduce competition among major carriers, thereby leading to higher prices and a decline in innovation.

Spokespeople for Sprint and T-Mobile did not immediately respond when asked to comment on the letter, but their executives have argued that the merger is necessary in order to compete with Verizon and AT&T when it comes to 5G network development.

The senators called those claims into question Monday and asked Delrahim and Pai to scrutinize what effects the deal would have on pricing, network expansion and innovation.

"The Department of Justice and Federal Communications Commission must carefully consider whether the proposed transaction may lessen competition or harm consumers," they wrote.