Boston police put two-year officer Justin Barrett on administrative leave Tuesday, pending a termination hearing.
Barrett is a captain in the Massachusetts National Guard, which also suspended him pending an investigation.
Barrett's Boston-based lawyer, Peter Marano, has scheduled a news conference Thursday afternoon. In an interview with WCVB-TV, Barrett, accompanied by Marano, said he was sorry about what he wrote.
"It was a poor choice of words. I did not mean to offend anyone," he told the station.
"I am not a racist, I never have been, never will be. I treat people with dignity and respect every time," he added.
Boston police said Barrett used a racial slur in a mass e-mail distributed to guardsmen, police officers and The Boston Globe.
Authorities are investigating Barrett's actions as an officer and talking to all recipients of the e-mail.
Police Commissioner Edward Davis said Thursday that Barrett's "venomous rhetoric" would not be tolerated and added that his hearing will take place in the next seven to 10 days. Union regulations prohibit the department from firing an officer immediately.
"His racist opinions and feelings have no place in our department," Davis said at a news conference.
The police commissioner said he spoke with Gates and his acting spokesman, Charles Ogletree, to apologize for the remark.
Barrett's union, the Boston Police Patrolmen's Association, said it condemns Barrett's words and called them "offensive and hurtful." But the union added that investigators should consider all the facts and not rush to a conclusion.
Barrett does not have previous violations with the department, police said.
Mayor Thomas Menino called for his dismissal from the force.
Gates was arrested in neighboring Cambridge on a charge of disorderly conduct at his home near Harvard University by a white police officer who was responding to a report of a possible burglary. The charge was dropped, but the case sparked a national debate over racial profiling.
Gates has no comment on Barrett, Ogletree told The Associated Press late Wednesday. Ogletree added that the e-mail "just tells you that there are some individuals who act completely out of character and it is not the sort of statement or a representation by police officers who I know -- and I know many -- or any police department that I work with, and I work with a lot."