Montgomery County disclosed Saturday it sent voters 16,000 incorrectly printed mail ballots for the Nov. 2 municipal general election, and county election officials said they were in the process of canceling them and will issue new ones.

It’s easy to identify the bungled ballots, officials said: They were printed on only one side.

The county’s ballot contractor, NPC, said in a statement that a programming error caused the back page of the ballot to be left blank.

“We sincerely regret that this happened and are working with the county and state to ensure impacted voters receive a new ballot,” company CEO Chip Gallagher said. “Once the error was recognized, we immediately stopped production and began to investigate.”

NPC, which prints and distributes ballots for a number of states and counties, among other services, is based in Claysburg, Pa., in Blair County.

In the Nov. 2 general election, voters will select a justice of the state Supreme Court, a judge on the appellate Superior Court, and two judges of the Commonwealth Court, which hears appeals on cases that involve state government. They also will be asked to decide whether two Superior Court judges and two Commonwealth Court jurists, and two Common Pleas judges in Montgomery County should be retained.

Also on the ballot are county judges — where there are open seats — municipal officials and members of school boards in districts where they are elected.

“This does not meet the standard we have come to expect from NPC,” said Dori Sawyer, director of elections for the county. “Upon notification of the error, we began working with the Department of State, taking the proper steps to cancel the incorrect ballots and issue replacements. We appreciate the patience of our voters while we reissue corrected ballots.”

Officials expect to mail replacements beginning next week. Voters who receive a one-sided ballot in the mail are asked to destroy it, the return envelope, and the envelope it came in, county officials said.

Voters who originally applied to vote by mail but choose not to return their mail ballot can vote in person Nov. 2. To do so, they can surrender their ballot and the return envelope at the polls — or cast a provisional ballot.

Residents with questions can submit a request online or call Montgomery County Voter Services at 610-278-3280.

This web page has sample ballots for Montgomery municipalities.