Sprint has become the latest company to file a lawsuit seeking to block AT&T's proposed acquisition of T-Mobile USA.
The telecoms firm said that the legal action opposes the deal on anti-competition grounds, arguing that the move will put Sprint and other carriers at a competitive disadvantage.
"Sprint opposes AT&T's proposed takeover of T-Mobile," said Susan Z. Haller, vice president of litigation at Sprint, in a statement.
"With today's legal action, we are continuing that advocacy on behalf of consumers and competition, and expect to contribute our expertise and resources in proving that the proposed transaction is illegal."
Sprint argues that the proposed deal will create a monopoly reminiscent of AT&T's 'Ma Bell' land-line system which was broken up in the early 1980s.
The lawsuit claims that many US consumers will be left with a choice of just two mobile carriers, Verizon and AT&T.
Sprint joins a growing list of companies and organisations opposed to AT&T's proposed acquisition.
Sprint's suit has been received as a "welcome addition" by those opposed to the AT&T/T-Mobile USA deal.
"The more the merrier. Sprint took on some issues that the Justice Department did not. It is a welcome addition to the issue," a spokesperson for consumer advocacy group Public Knowledge told V3.
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