NEWARK, N.J. – A major contributor to embattled Governor McGreevey pleaded guilty yesterday to charges stemming from a scheme in which he allegedly hired a prostitute to seduce his brother-in-law, a witness in the case.

Real estate mogul Charles Kushner pleaded guilty in federal court to 18 charges, including retaliating against a federal witness and violating campaign-finance laws.

Mr. McGreevey was not implicated in the charges, but the Kushner case was one of a series of scandals that clouded the governor’s future long before he announced his resignation last week.

“Mr. Kushner’s case has absolutely nothing to do with Governor Mc-Greevey,” Mr. Kushner’s attorney, Benjamin Brafman, said outside court.

Mr. Kushner also pleaded guilty to 16 counts of filing false tax returns through various real estate partnerships.

Mr. Kushner had been under federal investigation for about three years on the campaign contribution and tax fraud charges. He was then accused of hiring a prostitute to have sex with his brother-in-law, William Schulder.

Prosecutors said Mr. Kushner ordered the sex act videotaped and a copy of the tape sent to his own sister, Mr. Schulder’s wife, who also was cooperating in the investigation. The aim was to retaliate against the family members for cooperating with the government in the case.

U.S. Attorney Christopher Christie said Mr. Kushner faces 1 1 /2 to 2 years in prison, as well as “substantial” fines. The plea deal does not require Mr. Kushner to cooperate with investigators, and Mr. Christie said he did not expect Mr. Kushner to do so voluntarily.

Mr. Brafman said Mr. Kushner accepted responsibility and will be stepping down as chairman of his $1 billion company.

The plea comes six days after Mr. Mc-Greevey announced he was gay, said he had an affair with a man, and that he intends to resign November 15. Sources close to Mr. McGreevey have identified the man as Golan Cipel, an Israeli who held a state homeland security job in 2002.

While yesterday’s guilty pleas are unrelated to the McGreevey case, Mr. Kushner sponsored the work visa that allowed Mr. Cipel to come to America and gave him a $30,000-a-year job in public relations with one of his companies.

Mr. Cipel maintains he is heterosexual, and has denied Mr. McGreevey’s claims and accused the governor of sexual harassment.

Mr. Kushner’s attorney said his client had no contact with Mr. Cipel “for several years.”