What fredrich03 said is exactly right. Have the caliper rebuilt or by a new one. If its still under warranty have the dealer take care of the problem. Its a simple fix.I've seen this happen on motorcycles with a little age. Since caliper principles are the same, this may be the problem.
Corrosion builds in the piston seal groove, forcing the seal tighter and tighter in the caliper bore until the piston will not retract by itself.
I don't know if caliper rebuild kits are available for our cars. So, if it were me, I'd be looking for a new caliper.
Pretty sure I remember Vettes having this problem and went to stainless steel caliper pistons.