MINNEAPOLIS — A state board has asked the Minnesota Supreme Court to discipline a Twin Cities immigration attorney, saying he overcharged clients and then harassed them to pay up.

Herbert Igbanugo, 54, has 20 days to respond to the petition filed last week by the Office of Lawyers Professional Responsibility. The state Supreme Court will make the final decision on any discipline, which could range from dismissing the petition to disbarring Igbanugo.

Igbanugo took the unusual step of emailing the petition to the media, saying he was being targeted because he’s black and was born in Africa.

“The allegations are false, mean-spirited and deliberately stated out of context with evil intent and to inflict the highest damage to my reputation,” wrote Igbanugo, who was born in Nigeria.

The petition against Igbanugo was signed by Martin Cole, the board’s director and Cassie Hanson, the office’s senior assistant director.

“Our office denies any improper actions or biases against Mr. Igbanugo,” Cole said.

The petition alleges misconduct in three cases involving immigrants. It also lists three previous times between 2004 and 2009 that Cole’s office warned Igbanugo for alleged unprofessional conduct.

One case involved a Russian family whom Igbanugo helped receive asylum. He eventually sued them for more than $12,000 in unpaid fees and won, but the office said the litigation was frivolous and the fees were excessive.

Another case involved a Nigerian immigrant who retained Igbanugo’s services after the government challenged the validity of his marriage.

The immigrant retained Igbanugo and later challenged his billing fees.

Igbanugo wrote the man a letter saying, “You have mistaken my kindness for weakness. I did not get where I am today, allowing people, like you, to punk me. Perhaps you need to be taught a lesson in life.”

In his email to reporters, Igbanugo wrote that the truth will eventually clear his name. He said he’s served as many as 20,000 clients over a 25-year career and said that he handled the cases ethically and with good results.