While the company, Facebook, may not have any tax issues from the stock options, I'm quite certain the employees DO have a tax issue with the options. Once the employees buy stocks using the options (preferred share value over what is charged on stock market), the shares create an income tax issue (capital gain or loss) when they are sold.
IRS-the United States' national tax authority:
http://www.irs.gov/Help-&-Resources/Tools-&-FAQs/FAQs-for-Individuals/Frequently-Asked-Tax-Questions-&-Answers/Capital-Gains,-Losses,-Sale-of-Home/Stocks-(Options,-Splits,-Traders)
http://www.irs.gov/Businesses/Industry-Directive-on-Stock-Options-and-Cost-Sharing-Agreements
State of California, where Facebook is based:
Individual claims https://www.ftb.ca.gov/forms/2012/12_540d.pdf
Corporate claims https://www.ftb.ca.gov/forms/2012/12_568d.pdf