If the tax cut that was authorized was meant to be temporary, then no. It is not a tax increase once the authorized tax reduction period has expired but rather a reset of the taxes back to their original levels same as would happen if the Bush tax cuts were to expire January 1, 2013 (i.e., tax rate of 15% temporarily reduced to 12.5%; time period for temporary rate reduction expires, rates then return to original 15% rate).
A tax increase, IMO, would be if the rates were authorized at a higher level than what they were originally set (i.e., tax rate of 15% temporarily reduced to 12.5%, time period for temporary rate reduction expires, but new marginal tax rate of 18% is implemented).
The foremer scenario is what may happen if the payroll tax cut isn't extended. That latter isn't even being considered.
Reset...increase...too different things but both being viewed pretty much the same way because when you get right down to it both the reset and the increase takes money out of the pockets of working middle-class families who can least afford to pay more right now.
Note: I might also add that the argument concerning "defunding" the Social Security Trust Fund is also being misconstrued. No one's "raiding" the SSTF because no "stimulus" checks will be coming out from the Treasury that in anyway is associated with the payroll tax cut. (In short, no one is being paid anything to who otherwise would qualify for the payroll tax cut.) If anything, extending the payroll tax cut would be more like reauthorizing a payroll tax credit except all one has to do in order to receive the tax benefit essentially is be employeed.