The US Department of Justice (DOJ) has accused Apple of pursuing a campaign of character assassination against a Goodwin Procter partner appointed by a court to monitor the company's competition policies.

In a letter to court, seen by Legal Week, DOJ attorney Lawrence Buterman criticised Apple for its behaviour in making accusations that Michael Bromwich was biased and should be thrown off the monitoring role.

"Regrettably, it is now clear that Apple has chosen a campaign of character assassination over a culture of compliance," Buterman wrote last week.

"Apple has focused on personally attacking Mr. Bromwich, and thwarting him from performing even the most basic of his court-ordered functions."

Bromwich was appointed by a New York court in October to monitor the company's competition practices, following a ruling in July that Apple conspired with five publishers to fix e-book prices.

The comments are the latest in an ongoing spat between the technology giant, the DOJ and Bromwich, who is carrying out the monitoring work through his external consultancy group, alongside Fried Frank antitrust head Bernard Nigro.

In December, Apple objected to the fees charged by the group, which amounted to $140,000 (£85,000) in the first two weeks of instruction.

At the time, the company argued Bromwich's "personal financial interest is for as broad and lengthy an investigation as possible", and that his requests for interviews with senior Apple management were unnecessary.

This month, the Goodwin Procter white collar partner hit back at the claims by filing a series of email exchanges with the court, which he argues shows obstructive behaviour by Apple.

Apple then requested for Bromwich's disqualification from the monitoring role.

Government lawyers – including assistant attorneys general – on Friday called Apple's argument "pure sophistry", and urged the court to refuse the request.

"In Apple's view of the world, the fact that Mr. Bromwich did not sit silent and let Apple's misrepresentations lay unchallenged makes him biased and subject to disqualification," said Buterman.

"It is now apparent that Apple has no interest in resolving anything unless the resolution involves expunging the requirement of a monitor from the Final Judgment."

In an earlier filing, Bromwich quotes one senior Apple lawyer who told him the company's executives would "never get over the [e-books] case", and were still "extremely angry".

Apple could not be reached for comment.