According to Iowa law, people under the age of 18 are prohibited from working "in or about slaughtering and meat packing establishments." But rumors that teens were working at Agriprocessors and getting paid off the books had been circulating for months. No one will say just when the state and federal investigations into those rumors began.

What state officials will say is they're not getting much done on the case right now. "Due to this raid and the federal government confiscating all of those records, we're unable to complete our investigation at this time," said Neil.

That's exactly what the United Food and Commercial Workers Union was afraid of. Earlier this month the Union's Vice President wrote a letter to immigration and customs officials asking them to hold off on Monday's raid. The letter said "any potential ICE action could not only have a chilling affect over the existing workforce...ICE action could also result in employees leaving the plant...thereby interfering with the DOL's investigation that could ultimately uncover unscrupulous employer acts."

The one thing the raid did make clear is the investigation into child labor violations was warranted. Federal officials say up to a dozen minors were detained at the plant Monday between the ages of 13 and 17.