Three employees say they felt sick after a strange envelope with an oily residue was delivered to a federal immigration office in Durham.
WRAL-TV reports that Durham police evacuated the U.S. Bureau of Citizen and Immigration Service office on Tuesday after employees reported nausea and irritated eyes.
Three workers were taken to a local hospital as a precaution. Initial tests on the envelope did not find hazardous chemicals.
It's been sent to the state Division of Public Health for more tests.
Durham Police Captain D.C. Allen says the envelope had an odor, which might have sickened employees.
Immigration officials say operations were back to normal by Tuesday afternoon.