The complaint has been made by the National Association for the Advancement of Coloured People (NAACP), who claim that machines in two Georgia counties are switching Democrat votes to Republican votes.
A tightly fought contest is taking place for the Governorship of Georgia, with Democrat Stacey Abrams taking on Trump-backing Republican Brian Kemp.
Mr Kemp has been Georgia’s secretary of state since 2010, a position which makes him responsible for overseeing elections in the state.
According to the NAACP votes cast for Ms Abrams are being changed to Mr Kemp in Cobb and Bartow counties.
They claim some voters noticed the change and notified officials, but others may not have done.
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The NAACP have not said how many ballots they believe have been affected.
Mr Kemps campaign has said many of the incidents are either unconfirmed or the result of individual voter error.
One of those apparently affected was Pamela Grimes, who wanted to vote for Ms Abrams.
She said: “I was not going to leave until everything was the way I wanted it.
“If I had not been focused, my vote would have went for him.”
However, top NAACP official Gerald Griggs claimed: “The secretary of state knows we’ve had problems with these machines and to write it off as voter error is to just sweep under the rug the real problem with the machine.”
Mr Kemp is already facing legal action over claims his office has removed 340,000 Georgians from electoral rolls since 2010.
The lawsuit alleges this has disproportionately hit non-white voters in the state.
A separate legal case claims Mr Kemp’s officials have failed to register 53,000 new voters, predominantly from Democrat voting urban counties with high minority populations.
Should Ms Abrams win the election she will become the first black woman in US history to be elected as a state governor.
There have also been allegations of machines switching votes, both from Republican to Democrat and the other way around, in Texas.