A San Ramon divorce attorney charged with tax evasion and illegally bugging cars is expected to enter a guilty plea in federal court this month.

Mary Nolan, 61, of Oakland, was indicted by a grand jury in September 2012 on six counts related to accusations that she failed to report $1.8 million in earnings to the Internal Revenue Service and placed eavesdropping equipment on the cars of her clients' spouses with disgraced former Concord private investigator Christopher Butler. Court records show that she's scheduled to enter a guilty plea before Judge Charles Breyer on Sept. 27, although no details as to her plea agreement have been made public.

Nolan's attorneys could not be reached for comment Thursday. Assistant U.S. Attorney Hartley West confirmed that Nolan will plead guilty but declined to comment further.

Nolan has practiced law since 1983 and voluntarily inactivated her bar license Sept. 1, according to the State Bar of California.

Nolan also is a defendant in two of the half-dozen civil lawsuits pending in state and federal court lodged by the targets of Butler's "dirty DUI" stings in 2011 and 2012.

Butler's employees, usually attractive women, would entice the estranged spouses of Butler's clients to get drunk and drive, at which time Butler would encourage police to arrest the targets for DUI, giving his clients leverage in divorce and child-custody proceedings.

Nolan is accused of helping arrange the arrests of Concord aeronautics engineer Dave Dutcher and Clayton contractor Declan Woods, whose ex-wives, Susan Dutcher and Louise Woods, were represented by Nolan in family law court.

Authorities learned of the setups in February 2012 after Butler and former Contra Costa Narcotics Enforcement Team Cmdr. Norman Wielsch were caught selling drugs, leading to a countywide police-corruption probe and a host of criminal charges that put the former cops in prison for eight and 14 years, respectively.

Although numerous people were part of the "dirty DUI" stings, the only person prosecuted for them was former Danville officer Stephen Tanabe. He will be sentenced to prison time in December after his conviction earlier this month for accepting payment for facilitating three of the DUI arrests.

Nolan's charges call for a sentence of up to 15 years in prison and $750,000 in fines.

Contact Malaika Fraley at 925-234-1684. Follow her at Twitter.com/malaikafraley.