A nonprofit founded by Stacey Abrams, a Georgia Democrat, admitted on Wednesday that it had violated state law by concealing the fact that it had campaigned for her during her 2018 run for governor.

At the time of that campaign, the group was led by Raphael Warnock, who was later elected to the Senate as a Democrat from Georgia.

At a meeting of the state’s ethics commission, the nonprofit New Georgia Project conceded that it had paid for fliers and door-to-door canvassers telling voters to support Ms. Abrams and other Democrats.

Under federal law, tax-exempt charities like this one are forbidden to campaign for candidates, but this case was about a violation of state law.

The nonprofit conceded that, because of its campaign work for Ms. Abrams, it should have registered with the state as a political committee, but it did not. A related nonprofit, the New Georgia Project Action Fund, admitted the same.

As a result, the two nonprofits agreed to pay a $300,000 penalty. David Emadi, the executive director of the commission, said it was the largest fine in its 38-year history.