Congress agrees to keep the payroll tax (employee social security) rate at 4.2% UNTIL March 2012, instead of reverting back to the 6.2%. As a result, employees will see the same social security withholding in January and February as they did in 2011.If this did not happen, an average of a $1,000 tax increase for 160 million Americans would have taken place in 2012. This means that your paycheck would shrink by about $40 per pay period without this tax cut. There will be a further discussion of a year-long extension after the holidays when Congress reconvenes in January.

http://www.cnn.com/2011/12/23/politics/congress-payroll-tax-cut/index.html?hpt=hp_t1

http://online.wsj.com/article/SB10001424052970204552304577114394185169820.html?mod=WSJ_hp_MIDDLENexttoWhatsNewsSecond