By Jack Linshi, TIME

The U.S. Postal Service (USPS) revealed Monday that data on its employees may have been compromised in a “cyber intrusion incident.”

USPS said it recently learned of a data breach affecting the names, dates of birth, Social Security numbers, addresses, employment dates and emergency contact information of up to 800,000 employees.

Post office customers who contacted the Postal Service Customer Care Center via telephone or e-mail between Jan. 1 and Aug. 16 may have had their names, addresses, telephone numbers or e-mail addresses compromised, the USPS said, but added there’s no evidence to suggest customers’ credit card information was stolen or hacked.

“The intrusion is limited in scope and all operations of the Postal Service are functioning normally,” said USPS media relations manager David Partenheimer in a statement. “We began investigating this incident as soon as we learned of it, and we are cooperating with the investigation, which is ongoing. The investigation is being led by the Federal Bureau of Investigation and joined by other federal and postal investigatory agencies.”

Employees possibly affected by the data breach have been notified, and will receive credit monitoring services for one year at no charge, USPS said.

The mail service did not identify suspects in the investigation, but Partenheimer told the WashingtonPost that the intruder may be “a sophisticated actor that appears not to be interested in identity theft or credit card fraud.”