Voter Action Wisconsin said in its complaint to the state Elections Board that the machines are inherently unreliable, open to tampering and susceptible to human error.
The board didn't act on the complaint Wednesday, and several members said it would be unrealistic to instruct elections officials to switch to paper ballots or optical scan machines just 33 days before the election.
Board member Kerry Dwyer also said a switch would disenfranchise disabled voters who the machines were designed to help.
The complaint covers machines used at an estimated 1,300 polling places in 55 counties. Still, most Wisconsin voters will cast their ballots on paper or with optical scan machines.
Attorney Mike Wittenwyler, who represents Voter Action Wisconsin, acknowledged the board already requires safeguards, including a paper record of each vote made using the machines.
"But it still doesn't solve the inherent flaws of the machines," he said. "This is a system open to abuse, and it could be manipulated."
He said the group's complaint could turn into a lawsuit if the board refuses to act.
The machines are manufactured by Diebold Election Systems Inc., Sequoia Voting Systems, Inc., ES&S and Voting Technologies International.
Voter Action Wisconsin is part of Voter Action, a national nonprofit that has brought similar complaints in other states.