T-Mobile's proposed $26 billion acquisition of Sprint could result in "higher prices and fewer innovative services," Senator Ed Markey (D-Massachusetts) warns in a letter to the Senate Commerce Committee's leaders.
Markey is asking the committee's leadership to call a hearing to examine the wireless marketplace and evaluate the proposed merger.
T-Mobile said it had reached a deal to purchase Sprint. If the transaction goes through, the country will be left with just three major wireless carriers.
"To date, T-Mobile and Sprint have exerted competitive pressures on their larger rivals in the wireless telecommunications industry, helping drive down prices, eliminating harmful contract requirements, and making more expansive and consumer friendly data plans the norm," he writes.
Senator Elizabeth Warren (D-Massachusetts) has also expressed concern over the potential merger.
"The wireless business is already very concentrated -- there were six national companies as recently as 2003 -- and a deal that would further consolidate power is troubling," she writes in an op-ed in The New York Times. "Having fewer competitors emboldens businesses to raise prices and force consumers into long-term service contracts because they know that people don’t have many options."
Warren also notes that T-Mobile took a number of consumer-friendly steps -- including ones that left consumers able to change carriers without penalties -- after regulators said in 2011 that they would block a proposed merger with AT&T.
In recent years, Sprint and T-Mobile -- which both offer unlimited data plans -- appeared to spur Verizon and AT&T to beef up their data offerings.
Sprint and T-Mobile -- which have around 100 million customers between them -- attempted to merge in 2014, but regulators blocked the deal. It's not clear how the current administration will view the potential merger.