Officials in Chester County, Pennsylvania, have hired a law firm to investigate issues with poll books that affected third-party voters on Election Day this year. 

The county has appointed West Chester-based law firm Fleck Eckert Klein McGarry to independently investigate the issue, which forced thousands of voters to use provisional ballots on Election Day. 

The poll books omitted the names of more than 75,000 third-party registered voters, the announcement from the county says, including voters registered as Independent, Libertarian, Green Party, non-partisan and no affiliation.

Corrected books were delivered to polling places, and voting hours in Chester County were extended to 10 p.m. to help mitigate the issue.

Fleck Eckert Klein McGarry was one of 10 firms that submitted proposals for the investigation and was selected for its experience, independence and knowledge of election-related issues, the announcement says.

The investigation announcement comes after a hearing in which the county board of elections adjudicated about 1,400 provisional ballots that needed review, officials said. 

A provisional ballot is separate from a regular ballot and is typically cast at a polling place on Election Day when election workers need more time to determine a voter’s eligibility to vote. Voters can track provisional ballots online on Pennsylvania’s government website. Provisional ballots can take up to two weeks to be counted.

“We deeply regret the errors that occurred on and before Election Day, and through this review we commit to identifying the root causes of the problem and ensuring that it does not happen again,” Chester County CEO David Byerman said in a statement.

The investigation will focus on the cause of the incomplete books, the processes in place and why they failed, any other factors that contributed to the issue, and why it took so long for polling places to get corrected books. Investigators will also interview county staff and recommend improvements. 

The firm will complete a report on the investigation by Dec. 19 and make a presentation about it to a public Chester County Board of Elections meeting in January, the announcement says. The cost of the contract will not exceed $35,000.