Chancellor Angela Merkel's current and former chiefs of staff are appearing before a parliamentary committee over allegations Germany's spy agency acted against national interests in cooperating with U.S. counterparts.

The government has faced scrutiny over what the chancellery knew, and when, of the Federal Intelligence Service's activities since a report last month suggested it may have helped the U.S. spy on European companies and officials as long ago as 2008.

Merkel's then-chief of staff, Interior Minister Thomas de Maiziere, and incumbent Peter Altmaier were to testify behind closed doors Wednesday to the parliamentary panel overseeing intelligence services.

Merkel says she's willing to testify before a separate parliamentary inquiry. She's faced criticism over the reports but a poll Wednesday indicated the affair so far hasn't damaged her ratings or her party's.