MADISON, Wis. -- An internal investigation of a subcontractor for the Monona Terrace in Madison found at least a dozen people were undocumented workers, officials said.

An internal audit of all employees for Monona Catering, a separate company providing food services at Monona Terrace, found 12 workers whose names didn't match the Social Security numbers they provided. All

The catering company's general manager said the audit began in June and all employees with a so-called "no match status" were given 90 days to rectify the situation in compliance with union policy.

Initially, 14 employees were identified but two were able to correct clerical errors in their records.

Patty Lemke, of Monona Catering, said the audit was done voluntarily as part of a records update.

"We decided that this was a good time for us to be very thorough and go through all of our records and make sure we had everything just right," said Lemke. "We were very methodical about how it was done and started with management, of course, and went through our different job classifications; just batch by batch."

The 12 employees were either part-time or extra help hired for large events by the catering company. A few new employees have been hired in their place.