The chairman of Citigroup's audit and risk committee, Michael Armstrong, is expected to step down from the post, as the company faces pressure from shareholders who think the board deserves blame for Citigroup's recent woes, according to people familiar with the matter.

Armstrong, the 69-year-old former chief executive of AT&T, is expected to remain on Citigroup's board after relinquishing the audit committee chairmanship, which he's held since 2004. It's not clear who will replace him as chairman.