The recent "fiscal cliff" bill did not extend the payroll tax cut. Congress did not extend the 2 percentage point reduction, so that's why you're seeing a reduced pay check. It's not FCPS, it's the Social Security tax.
http://www.washingtonpost.com/blogs/wonkblog/wp/2013/01/11/ouch-no-youre-not-imagining-it-your-paycheck-just-shrunk/?wprss=rss_homepage