New union president was elected by narrow margin, then extra ballots were found.
GM has said the expansion will create up to 1,850 jobs for the region.
Voters in both Kansas City and St. Louis approved retention of their earnings taxes in April.
The lockout has already lasted 13 months, and now the vote on the contract proposal has been postponed.
The five-term Republican has been voting from the address of his old family homestead in another suburb
City council votes 6-1 Monday to approve registry for domestic partnerships.
The legislation would require voters to show a government-issued photo ID to cast ballots.
Steady stream of voters were passing through doors of south St. Louis polling place.
Voters in St. Louis, KC will decide future of 1% earnings tax.
St. Louis, KC face crucial April vote on taxes.