You certainly don't need to take it to bare metal and you won't likely have to take all the paint off.
What you will need to do is determine if the coating is tightly adhered or not. A pressure washer is a good start as is will peel off a delaminating coating very efficiently. A razor blade will also strip clean the clear coat if it's not sticking, but won't if it is.
Any new coating can stick to a previous coating so long as it's "tightly adhered"... this is the sticky point... (pun intended)
Once you determined that the clear is sticking in areas or not, you'll have to feather edge the areas where the clear is "tightly adhered" to make a smooth surface. You should apply a high build primer and fix any dents or imperfections while you are at this stage since you are painting it anyway. NOTE: Chances are that the entire area that's starting to peel will be a problem for the entire panel so you might just as well sand all the clear coat off to base coat.
I know this sounds like a lot of work, which it is, but new clear won't glue down failing clear.
The reasons the clear is peeling can be many, but in my experience, the base coat was left too long before the clear was applied and therefore, cohesion was not accomplished. (Cohesion is the term for inter-coat adhesion)
Just my 2 cents.