May 29 (Reuters) - Facebook has received notice that U.S. antitrust regulators will give its proposed purchase of the popular photo-sharing app maker Instagram a lengthy investigation, an industry source told Reuters on Tuesday.
Facebook has received a "second request" from the Federal Trade Commission, essentially a request for relatively large amounts of data that the regulators will sift through to ensure that the deal complies with antitrust law.
A prolonged review adds another headache to the No. 1 social network, whose shares on Tuesday slid below $29 to a new low as nervous investors continued to show their concerns about Facebook's long-term business prospects and its rich initial public offering price of $38.
Facebook announced in April that it would purchase Instagram for $1 billion in cash and stock, in its largest-ever acquisition.
The "second request" letter from the FTC is dated May 16, the source said.