Paraphrased from the Wall Street Journal:
The fiscal cliff deal did not extend the payroll-tax holiday. The biggest hit to 2013 growth appears likely to come from this tax break’s expiration on Jan 1 2013.
The workers’ share of the Social Security payroll tax had been lowered by two percentage points for the past two years, to 4.2% from 6.2%, amounting to an annual income boost of $1,000 for a typical U.S. family earning $50,000 a year. It provided an increase of as much as $2,202 this year for a worker earning $110,100, the maximum wage subject to the payroll tax.
The end of the tax break effectively raises taxes for all wage earners this year.