Missoula County election officials discouraged some poll watchers who were threatening to challenge every ballot cast after 8 p.m.
About 275 people were still waiting to register to vote in the Fine Arts building of the county fairgrounds when election officials announced no more people would be allowed to join the line.
But they told everyone already present that the polls would remain open until all of the line had voted.
Senior Deputy County Attorney Dori Brownlow said election workers at the fairgrounds reported the poll watchers' intention to challenge the ballot of every person who wanted to file a late registration. She advised them that wouldn't win a legal battle.
"The election administrators have determined their (the poll watchers') challenge would be insufficient if they (the prospective voters) were in line to register," Brownlow said on Tuesday evening. "They have the right to register and the right to vote. This is how it has always been."