Cohen has been ordered to appear Monday in federal court in NY for arguments over last week's raid.
Prosecutors say they are investigating Cohen's personal business dealings.
"The appearance of fairness and justice is compromised by the government's use of the its own personnel to review potentially privileged material", Hendon wrote.
The government's current approach to the case is to have a special team review the documents, to make sure that those conducting the actual investigation don't see the privileged materials. Not only has its use been controversial, but the information Cohen alleges to be "fake news" has turned out to be anything but in some cases. The FBI reportedly raided his office and residence a week ago looking for information pertaining to the Daniels payment and the one given to a former Playboy Playmate, Karen McDougal, who claims she had a monthslong affair with Trump between 2006 and 2007.
The hearing in a New York City courtroom stems from a surprise raid this month on Cohen's home and office. The documents seized in the raid could very well include the conformation to the alleged $130,000 paid as "hush money" to adult actress Stormy Daniels for her affair with Trump in the final days of his presidential election campaign in 2016. Cohen will not be alone at that hearing, scheduled for 2 p.m. today: In tweets over the weekend, a lawyer for Stephanie Clifford, the porn star better known as Stormy Daniels, said Clifford would be there too, setting up a remarkable face-to-face confrontation. But he said he never retained Cohen "in any traditional sense", never paid him and never got billed for a legal fee.
Trump's attorneys argue that he and Cohen should not have to rely on the government's "clean team" to review the documents to protect his privilege, as he has "a unique interest in ensuring that every privileged item is fully protected from improper disclosure". Mueller's team recently told Trump's lawyers that he is a subject of the investigation, but not a criminal target.
Last week, he filed a motion to prevent materials seized in an Federal Bureau of Investigation raid of his office and home from being used, citing attorney-client privilege.
The request comes after Cohen's home, hotel room, and office were raided by F.B.I. agents on April 9.
The next phase is a battle over the procedures involving who may review the materials seized by FBI investigators last week. They claim it's protected by attorney-client privilege.
Though President Trump declared after last week's raids that "attorney-client privilege is dead", there's actually a higher bar for obtaining a search warrant that might scoop up privileged materials.
Trump's personal lawyers argued Sunday that the Justice Department can't fairly evaluate whether Cohen's records are protected by attorney-client privilege, given the "staggering amount of attention trained on this investigation, Mr. Cohen, and the president". Cohen's lawyer is asking for the lawyers themselves to review the material or a "special master" to decide what is relevant to the case, and Hendon is concerned about a taint team or however the material is handled.