A Republican-appointed judge with extensive antitrust experience was selected on Tuesday to preside over the U.S. government's lawsuit to block AT&T Inc's acquisition of Time Warner Inc, sending Time Warner shares higher as investors bet the judge would be more likely to allow the deal to proceed.

Judge Richard Leon, a senior judge on the District of Columbia District Court, who was appointed by President George W. Bush in 2002, was assigned to the case after it was initially allotted to Judge Christopher Cooper, an Obama administration appointee.

Judges for antitrust cases are selected randomly. No explanation was given as to why the case was reassigned. Republican-appointed judges are generally, but not always, more business-friendly than those appointed by Democrats.

Shares of Time Warner added to gains after Leon's selection, and were trading up 2.5 percent at $89.86 at midday, signaling that investors believe the deal has a better chance of being approved.

The U.S. Department of Justice on Monday sued AT&T arguing that the U.S. No. 2 wireless carrier would use Time Warner's content to force rival pay-TV companies to pay "hundreds of millions of dollars more per year for Time Warner's networks."

AT&T has vowed to defend the US$85.4 billion deal.

The Department of Justice's move to block it was "foolish" because the deal posed no threat to consumers, the wireless carrier's trial lawyer Dan Petrocelli told CNBC on Tuesday.

"We want to go to court as soon as possible," Petrocelli told CNBC, saying the burden of proof was on the government.

AT&T will ask the court for an expedited trial next week, a source familiar with case said.

The Justice Department has not successfully litigated to stop a vertical deal - where the merging companies are not direct competitors, as is the case with AT&T and Time Warner - since the 1970s, when it prevented Ford Motor Co from buying assets from spark-plug maker Autolite.

The case will be closely watched because U.S. President Donald Trump has been a vocal critic of Time Warner's CNN, and opposed AT&T's purchase of Time Warner on the campaign trail last year, saying it would concentrate too much power in AT&T's hands.