In its revised S-1 filing with the Securities and Exchange Commission (SEC), Facebook was forced to admit that as a result of an investigation by the FTC, it may face a six-month wait until it can finalise its $1 billion cash and shares deal for Instagram.

The form, which was submitted earlier this morning, amended wording that stated when the company expected the deal to close, changing its prediction from a second-quarter closing to a more generic “close in 2012.”

Filed under Liquidity and Capital Resources, the differences between the two forms are detailed below:

Old:

This acquisition is subject to customary closing conditions, including the expiration or early termination of all applicable waiting periods under the Hart-Scott-Rodino Antitrust Improvement Act of 1976, as amended (HSR), and is currently expected to close in the second quarter of 2012.

New:

This acquisition is subject to customary closing conditions, including the expiration or early termination of all applicable waiting periods under the Hart-Scott-Rodino Antitrust Improvement Act of 1976, as amended (HSR), and is expected to close in 2012. 

The FTC launched a “competition probe” into Facebook’s recent acquisition of Instagram, commencing an investigation could take upwards of six to twelve months, delaying the close of the sale, which Facebook believed would be finalised before the end of June.

The acquisition was seen as putting Facebook on a faster track for mobile dominance, but the company must wait until the deal goes through to integrate the service into its own in any way.

The probe, which is standard for a size of this deal, will consist of the FTC gathering information from Facebook’s competitors, as well as looking at the overall impact of the acquisition itself.

Relating back to Facebook’s IPO, its Class A common stock has been approved for listing on NASDAQ under the symbol “FB”. In total, Facebook will offer just south of 337.5 million shares to potential investors.

At the high end of the $34 – $38 price range, the offering would value Facebook at more than $100 billion. The IPO would net Facebook $6.4 billion in proceeds, assuming a midpoint $36 per-share price.

The social network boasts over 900 million monthly active users, 526 million daily active users on average and roughly 488 million monthly active mobile users.

Previously, Facebook said it intended to price its shares between $28 and $35, which would have valued it between $77 billion and $96 billion.