AT&T has a new investor breathing down its neck. Hedge fund Elliott Management led by billionaire Paul Singer disclosed Monday it has taken a $3.2 billion stake in the telecom giant and called the company "deeply undervalued." And it wants to see changes.

It's questioning AT&T's $85 billion takeover of Time Warner, saying it hasn't provided a strategic rationale for owning the company behind CNN and HBO. Elliott hinted it wants seats on the board, and it called on the wireless carrier to sell non-core businesses to boost its stock price. Among the possible sales candidates Elliott cited: satellite service provider DirecTV and regional sports networks.

AT&T said it would engage with Elliott and review the investor's perspectives.

News of Elliott's demands lifted AT&T shares to their highest levels in a year.

President Donald Trump, a frequent critic of the news network CNN, welcomed Elliott's intervention, tweeting, "Great news that an activist investor is now involved with AT&T." He called on the fund to make changes at CNN.

His administration tried to block AT&T's purchase of Time Warner but the deal won court approval last year.