A criminal investigation is underway in Pennsylvania's crucial presidential race after election workers in one county flagged about 2,500 voter registration forms for potential fraud. Two other counties were alerted to check for similar problems.

The forms arrived at the Lancaster County election office last Monday just before the state's deadline for registration and appeared to be part of a larger effort to register people, officials said Friday. Some had false names, suspicious handwriting, questionable signatures, incorrect addresses or other problematic information.

Two other counties “received similar requests” and were asked to review them, Lancaster County District Attorney Heather Adams said at a news conference. She declined to name the other counties.

“At this point it appears to be an organized effort,” said Adams, an elected Republican. “But of course it is an ongoing investigation. And we will see who exactly took part and how far up it goes.”

The applications were separated during the investigation to prevent ballots from being sent to or cast by people until they were deemed valid. A battle is underway for Pennsylvania's 19 electoral votes as polls suggest the state's presidential contest is a close race.

“The fact is we have contained this,” Lancaster Commissioner Ray D'Agostino, a Republican and chairman of the Board of Elections, said at the news conference. “That is not right. It's illegal. It's immoral. And we found it, and we’re going to take care of it.”

Adams and county election board members did not say who submitted the forms or who they may have worked with.

D'Agostino said the petitions were not limited to a single party and were collected from various locations in majority-Republican Lancaster.