Walgreen has faced pressure from many sides and last month scrapped a plan to move its tax domicile to Europe to save money.

It also replaced its chief financial officer in August, two days before it lowered an earnings projection.

In a Sept. 11 letter to Walgreen's audit committee chair, CtW asked for more details such as when committee members learned the company's performance was not on track.

The group also asked the board for changes that could make it easier for shareholders to elect certain directors. They cited the recent naming to the Walgreen board of Barry Rosenstein, who founded activist hedge fund Jana Partners. CtW said Jana's presence could "further dilute the voice of long-term shareholders."

CtW said it advises funds that own about 2.5 million Walgreen shares, less than 1 percent of those outstanding.

Walgreen spokesman James Graham said in an email that the company will share the letter with its board and respond appropriately, "In accordance with our normal practice and our commitment to engage with our shareholders."

Regarding the director-election changes, Graham noted a shareholder proposal calling for so-called "proxy access" did not pass at the company's annual meeting in January.

A Jana spokesman was not available to comment.

(Reporting by Ross Kerber; Editing by Andre Grenon and Lisa Shumaker)