The escalating battle between No. 2 U.S. mobile service provider AT&T Inc (T) and smaller rival T-Mobile US (TMUS) got personal on Monday night when the bigger operator kicked T-Mobile's outspoken Chief Executive John Legere out of its party at the Consumer Electronics Show, according to Cnet.com.

The latest sign of an increasingly testy relationship between the two companies, which tried to merge in 2011, comes as they fight for each other's customers. AT&T said last week it would pay T-Mobile customers to switch.

According to a Cnet.com report, Legere was escorted out of the Las Vegas event by security guards about 15 minutes after Cnet reporter Roger Cheng posted a picture of himself and Legere and tweeted that the executive had crashed AT&T's party wearing his trademark pink T-Mobile t-shirt.

Around the same time that Legere was being escorted out, AT&T's mobility chief Ralph de la Vega was announcing that his company had won a deal to provide wireless connections to Audi vehicles, beating T-Mobile US, Cnet reported.

According to the Cnet report, Legere went to the party because he wanted to see a performance by rapper Macklemore, whose agent gave the executive and his entourage a pass for the party.

While AT&T and T-Mobile did not respond to requests for comment, Legere retweeted multiple tweets about the incident, including Cheng's tweet that Legere was kicked out.

Legere, an outspoken critic of his industry rivals, spent most of 2013 directly marketing against AT&T in particular. AT&T is most vulnerable to competition from T-Mobile because both companies have the same network technology, which makes it easy for consumers to switch between their services without having to buy new phones.

AT&T fought back by launching an offer on January 3 to T-Mobile customers for a $200 credit if they switch to AT&T. Legere responded in a tweet directed at AT&T Chief Executive Randall Stephenson asking "do you really think you can buy them back?"

Legere has been tweeting heavily to build up anticipation for his company's next competitive move, which is to be announced at a January 8 CES press conference.

(Reporting by Sinead Carew; Editing by Dan Grebler)