D.C. limits cash donations at $25. The Washington Post reports the Gray campaign converted a number of cash donations into money orders, which have a higher limit.
The mayor says if mistakes were made, the people responsible will be held accountable.
"So that there are allegations of impropriety -- we want to get to the bottom of that also -- we want answers and we will fully cooperate as we have thus far with any investigations," Gray says.
Gray says he regrets that unresolved issues from his campaign continue to surface.
The U.S. attorney's office is investigating claims that Gray's campaign promised a job and gave cash - including money orders - to a minor candidate so he could stay in the race and verbally attack then-Mayor Adrian Fenty.