They are demanding that satellite, early voting offices be opened immediately after Circuit Court Judge Lorenzo Arredondo on Monday ordered they should be opened under Indiana law, saying all elections shall be fair and equal.
But during the union representatives' news conference, the federal judge who has been on the case since Friday, trumped that decision and vacated any action by any other circuit or state courts.
A decision by the federal court could affect turnout in a key swing state in next month's presidential election.
Republicans have argued that the satellite centers in Gary, Hammond and East Chicago are illegal. They say there was no bipartisan vote to approve them.
Democrats argue that this is an effort to hold down voting in Democratic areas.
"This is an egregious act to suppress the vote. This is the equivalent of sending the American voter to the back of the bus," said Bishop T. Lane Grant.
"There are plenty of options. The idea that somebody is not able to vote because of this, I think, is a misnomer," said David Brooks, attorney for Lake County, Indiana GOP.
Before the federal judge took over the case, Lake County Democrats and Republicans were battling it out in yet another court. An East Chicago superior court judge had issued a Temporary Restraining Order on the satellite voting centers opening.
The federal court hearing will resume on Friday at 9 a.m. Until then, the satellite offices are not scheduled to be up and running until Tuesday October 14. Friday's hearing could change that.