Michael Bromwich, who became Apple's monitor after it was found liable for conspiring to raise ebook prices, said in a report on Thursday that Apple objected to providing information and "inappropriately" attempted to limit his activities.
Bromwich, whose relationship with Apple has been testy since the start, had indicated that relations had improved in a report in October to U.S. District Judge Denise Cote in Manhattan.
However, he said in his latest report that the company recently had taken a more "adversarial tone" in discussions.
"We have conducted no interviews since January, and Apple has rejected our recent requests for interviews," Bromwich wrote.
Despite those difficulties, Bromwich said he had interviewed Apple's entire board and executive team, and Apple had made progress in developing a "comprehensive and effective" compliance program.
Representatives for Apple did not immediately respond to requests for comment.
Bromwich, a former U.S. Justice Department inspector general, was appointed by Cote in October 2013 after she found the company liable in the civil antitrust case brought by the Justice Department.
The publishers include Lagardere SCA's Hachette Book Group Inc, News Corp's HarperCollins Publishers LLC, Penguin Group Inc, CBS Corp's Simon & Schuster Inc and Verlagsgruppe Georg von Holtzbrinck GmbH's Macmillan.
Apple has appealed, arguing it engaged in pro-competitive conduct when it entered an ebooks market in 2010 dominated by Amazon. During arguments in December, a three-judge panel appeared sympathetic to Apple's arguments.
If Apple wins the appeal, it could jeopardize a related $450 million settlement among Apple, 33 attorneys general, and lawyers for a class of consumers.
A separate appeal by Apple seeking to disqualify Bromwich was heard in March. Apple said Bromwich has been overly aggressive in seeking interviews with executives and engaging in private discussions with the Justice Department.
Apple has also objected to Bromwich's fees, initially $1,100 an hour before being reduced to an undisclosed amount.
The case is U.S. v. Apple Inc, U.S. District Court, Southern District of New York, No. 12-02826.
© Thomson Reuters 2015