Kansas City, Kan. — Government attorneys say a federal judge exceeded her authority when she ordered the Department of Justice to pay an expert to investigate possible breaches of attorney-client privilege at a private Kansas prison.

In a motion filed late Thursday, federal prosecutors claimed sovereign immunity, called the probe’s anticipated cost excessive and unreasonable, and said the case isn’t the right place to address the practices of an independent contractor.

Earlier this month U.S. District Judge Julie Robinson appointed Ohio attorney David R. Cohen as special master to review hundreds of hours of video and audio recordings at the Corrections Corp. of America prison in Leavenworth. She set his pay at $500 an hour and ordered the government to foot the bill.

Defense attorneys pushed for an investigation after discovering that their meetings with clients in conference rooms at the prison were being recorded without audio. They were further alarmed when they found out that some of their phone conversations with inmates also were being recorded without their knowledge.

The recordings came to light in August after federal prosecutors tried to force a defense attorney off two cases using footage subpoenaed by a grand jury in a broad contraband probe at the prison, according to court documents.

Prosecutors told Robinson last month they did not consent to her appointment of a special master under the parameters she set — including possibly having Cohen investigate the actions of some of the prosecutors themselves.

They estimated Cohen’s investigation could cost well more than $1 million, but noted that even if it were only half that, $500,000 would represent 120 percent of the Kansas office’s budget this fiscal year for litigation-related expenses.

Cohen met with attorneys on both sides of the case for the first time Friday to discuss information he was seeking from them.

Robinson said she would hear the government’s motion to reconsider after the federal public defender’s office has a chance to file a response.