(Reuters) – Election authorities in Georgia have opened investigations into third-party groups trying to sign up new voters in advance of a January special election that could determine control of the U.S. Senate, Secretary of State Brad Raffensperger said on Monday.

Raffensperger said his office was examining registration efforts by America Votes, Vote Forward and the New Georgia Project. He said some groups had been encouraging people who lived outside Georgia to register to vote in the state.

“These third-party groups have a responsibility to not encourage illegal voting. If they do so, they will be held responsible,” he said.

Raffensperger said his office also had several investigations open into accusations of wrongdoing in the U.S. presidential election.

(Reporting by Brad Heath; editing by Jonathan Oatis)