Leap Wireless International, the parent company of prepaid carrier Cricket Communications, has officially joined the ranks of companies against AT&T’s $39 billion takeover of T-Mobile USA.

“We oppose the proposed acquisition,” Leap President and CEO Doug Hutcheson said in a statement.

Hutcheson argued the merger of AT&T and T-Mobile would concentrate spectrum assets in the hands of fewer companies; impair smaller operators’ ability to buy new spectrum; undercut access to wholesale voice and data roaming services; lower the amount of devices available to Tier 2 operators and reduce the interoperability of wireless networks and devices.

If regulators approve AT&T’s acquisition of T-Mobile, the company will become the largest carrier in the country with a combined customer base of more than 120 million subscribers, surpassing Verizon Wireless. By comparison, Leap had just 5.8 million customers through its Cricket prepaid brand at the end of the first quarter.

Leap’s formal opposition to the deal comes after several of AT&T’s smaller competitors asked regulators to block the deal.

Sprint, Cellular South and the Rural Cellular Association have launched an all-out assault on the deal, lobbying lawmakers and regulators, making regular pitches to the media and petitioning states to open investigations into the merger.

Sprint has called AT&T’s buyout of T-Mobile “anticompetitive,” saying the deal will give AT&T and Verizon a near-duopoly hold on the U.S. wireless market. If the merger passes government scrutiny, AT&T and Verizon will have a combined market share of about 80 percent.

AT&T’s pledge to expand its LTE network to underserved areas if its deal with T-Mobile goes through helped it land support for the merger from the NAACP. The AFL-CIO and the Communications Workers of America (CWA) also support the merger.