Sprint, which has opposed rival AT&T’s proposed $39 billion purchase of Bellevue-based T-Mobile USA since the beginning, this morning announced that it’s filing its own lawsuit against the deal, following up on the U.S. Justice Department’s bid to block the acquisition in court last week.

“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,” said Susan Z. Haller, Sprint’s vice president for litigation, in the news release announcing the suit.

AT&T and Deutsche Telekom, T-Mobile USA’s parent company, vowed last week to continue fighting for the deal despite the Justice Department’s suit.

Under their agreement, AT&T could end up paying Deutsche Telekom a $3 billion breakup fee if the deal falls through.

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