Democrats want T-Mobile to promise not to lay-off workers

"Experience has shown that companies often achieve these savings through job cuts and employee lay-offs," the lawmakers wrote. 

They noted that both MetroPCS and T-Mobile have closed customer call centers and shipped them overseas in recent years.

They said the FCC, which is currently reviewing the deal, should force T-Mobile to commit to "preserving U.S. jobs" to receive approval.

The letter was signed by Democrats including Reps. Ed MarkeyEdward (Ed) John MarkeyGOP senator announces bill to block companies from tracking online activity Trump faces criticism for hosting Hungary's leader Bill Nye tees off on climate change skeptics: 'The planet is on f---ing fire!' MORE (Mass.), Jan Schakowsky (Ill.), John Conyers (Mich.) and Elijah Cummings (Md.). The Communications Workers of America, the industry's largest union, also supported the letter.

The merger between T-Mobile, the smallest of the four nationwide carriers, and MetroPCS, which specializes in pre-paid services, has generated little opposition from consumer advocates. 

The deal would strengthen T-Mobile's position as it struggles to compete with industry giants AT&T and Verizon.

“The combination of T-Mobile USA and MetroPCS will create a stronger company with the goal of emerging as the country's leading value carrier, providing much needed competition against the larger established players in the wireless business," Timothy O'Regan, a T-Mobile spokesman, said in a statement. 

He argued that the evidence before the FCC "clearly demonstrates" that the deal is in the public's interest. 

"Importantly, no one opposed our transaction at the FCC on any grounds, and the Commission should move expeditiously to approve our merger,” he said.