Facebook’s $1 billion purchase of photo-app Instagram caused quite the uproar in Silicon Valley, but it apparently also raised the eyebrows of federal regulators.

Now, just eight days away from Facebook’s scheduled IPO date, we’re hearing the Federal Trade Commission is looking into the social network’s acquisition of Instagram.

Two sources tell the Financial Times the FTC is investigating the deal for possible antitrust issues. Given that, from what we learned exclusively a few weeks ago, the deal was created in order to stick it to the competition, it’s not an unreasonable set of questions to ask.

The FTC is reportedly questioning some of Facebook’s biggest competitors — we’re looking at Google and Twitter, in particular. But in fact, such probes are routine for acquisitions worth more than $66 million or so, and this deal most certainly fits into that category.

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Facebook paid $300 million in cash for the photo-sharing app, as well as 23 million shares of Facebook common stock — and Lord knows how much that will be worth after May 18 when the stock goes public.

Based on the starting price range of $28-$35 per share, Instagram stands to get between $644 million and $805 million from the second the bell rings on the 18th. By the time trading closes, there’s no telling how much the deal will be worth; however, we’re fairly certain that those 23 million shares will be far more valuable than the original $1 billion quoted as Instagram’s pricetag for this acquisition.

If the FTC doesn’t green-light the deal, Facebook will pay out a $200 million breakup fee, as stipulated in the social network’s amended S-1 filing.

Facebook’s Instagram acquisition was expected to close in the second quarter of the year; an FTC probe could, but may not necessarily, delay the deal’s closing. We have not yet heard if the FTC’s questioning will have any impact on Facebook’s IPO timing.