The suspicions arose “a few weeks ago”, and the company has alerted the authorities in the southern German city of Munich, an Airbus source said.
“Some of our employees had documents that they shouldn't have had,” the source said.
The employees work in the Munich-based Programme Line Communications, Intelligence and Security (CIS), which handles cybersecurity and related activities.
Airbus said it was conducting an “ongoing internal review with the support of an external law firm” in the case.
“The company is fully cooperating with relevant authorities to resolve the matter,” it said in a statement.
It said it had “self-declared to German authorities potential wrongdoings by several employees with respect to certain customer documents relating to two future German procurement projects” handled by CIS.
Munich prosecutors could not be reached for comment late Wednesday.
The German daily Bild reported that around 20 Airbus employees were immediately suspended and that investigators had seized files and computers.
Bild said the employees had obtained secret files of the German army involving the acquisition of a communication system, among other subjects.
The army disciplined one employee, Bild reported.