Every Democratic senator currently running for president is opposed to the $26 billion merger between T-Mobile and Sprint.

Sens. Cory Booker (D-N.J.), Kirsten Gillibrand (D-N.Y.), Amy Klobuchar (D-Minn.) and Elizabeth Warren (D-Mass.) signed a letter from Sen. Richard Blumenthal (D-Conn.) calling on Federal Communications Commission Chairman Ajit Pai to reject the merger between the third- and fourth-largest mobile service provider in the United States.

The proposed merger would leave Americans with just three wireless carriers with all the incentives to squeeze consumers for more money through increased prices and unnecessary fees, the letter argues. If approved, the merger would create a country-club market in which Verizon, AT&T and the new T-Mobile/Sprint could divide the market, and collect ever-rising monthly rents from wireless subscribers with few real alternatives, according to the letter. (Verizon owns HuffPost.)

Sen. Kamala Harris (D-Calif.) who did not sign the letter agrees with concerns expressed in the letter and hopes the Department of Justice rejects the proposed merger, according to a statement from Chris Harris, a spokesman for her Senate office.

Additionally, two potential but yet-unannounced Democratic presidential candidates, Sens. Sherrod Brown (D-Ohio) and Bernie Sanders (I-Vt.), also signed the Blumenthal letter.