Senate Democrats are urging the Federal Communications Commission and the Antitrust Division of the Department of Justice to closely consider whether T-Mobile’s planned acquisition of Sprint will hurt competition and harm consumers.

In a letter delivered on Monday, Sen. Amy Klobuchar (D-Minn.) spearheaded a group of senators who expressed their concerns to leadership at both agencies. The transaction, they say, would combine T-Mobile, the third-largest wireless carrier in the United States with over 72 million customers, with Sprint, the fourth-largest wireless carrier with over 54 million customers, reducing the number of wireless carriers from four national competitors to three.