(Reuters) -Activist investor Elliott Investment Management has built a sizeable stake in Starbucks ( SBUX ), a source told Reuters on Friday.

The Wall Street Journal had first reported on the development.

Elliott has been engaging with the coffee chain behind the scenes in recent weeks, according to the WSJ report, which said that the activist has been pushing Starbucks ( SBUX ) privately to boost its stock price.

Shares of Starbucks ( SBUX ) were last up over 5% in afternoon trading.

Starbucks ( SBUX ) and Elliott did not immediately respond to Reuters requests for comment.