Boston (CNN) - Voters at three different places received ballots already marked for Republican candidate Scott Brown in Tuesday's special U.S. Senate election, according to campaign officials for Democratic candidate Martha Coakley.
At a news conference less than three hours before polls closed, Coakley campaign attorney Marc Elias said the campaign notified the Massachusetts secretary of state of what he called spoiled ballots that should not be counted.
Brian McNiff, a spokesman for the Massachusetts secretary of state's office, said it received two reports of voters saying they received pre-marked ballots.
The voters received new ballots to cast, and the ballots in question were invalidated, McNiff said.
Kevin Conroy, the Coakley campaign manager, said the "disturbing incidents" raised questions about the integrity of the election. In response, the Brown campaign issued a statement criticizing Coakley's team.
"Reports that the Coakley campaign is making reckless accusations regarding the integrity of today's election is a reminder that they are a desperate campaign," Daniel B. Winslow, the counsel for the Brown campaign, said in the statement.
Brown and Coakley are running for the Senate seat formerly held for more than four decades by liberal Democrat Ted Kennedy. The race is surprisingly tight, with Brown surging from behind in recent weeks.
A Republican victory in the Democratic stronghold would imperil the agenda of President Barack Obama by stripping Senate Democrats of their 60-seat super-majority needed to overcome a Republican filibuster.
Elias was the lead attorney for Sen. Al Franken, D-Minnesota, in his protracted election battle that prompted a court fight before Franken was declared the winner months after the November 2008 vote.
–CNN's Jessica Yellin contributed to this report.