Domenici acknowledged in March 2007 he contacted the prosecutor, asking about the status of an investigation involving Democrats.
McClatchy Newspapers had reported that Domenici and Rep. Heather Wilson, R-N.M., pressured former U.S. Attorney for New Mexico David C. Iglesias to expedite indictments of a Democratic politician prior to the 2006 election.
Wilson was involved at the time in a hotly contested re-election campaign, which she won by 875 votes out of more than 210,000 cast.
After saying he didn't know what Iglesias was talking about, Domenici admitted making a call but denying he pressured the former prosecutor.
"In retrospect, I regret making that call and I apologize," Domenici said.
The ethics panel's decision to issue a "qualified admonition" means it did not feel the evidence was strong enough to take stronger action, but was not prepared to let Domenici off without consequences, The Politico reported.
Domenici has said he urged Justice Department officials to replace Iglesias, but he said that occurred before he called Iglesias about the corruption investigation.