ESPP discount deemed ordinary income when sold - do I have to pay FICA on that when I am retired?

I am retired but still have some ESPP stock from my last two employers. I know that when I sell these ESPP shares the 15% discount I received will be deemed "ordinary income" and as such I will need to pay federal and state taxes.

My question is do I also have to pay FICA on this as well? 

I have no other "earned income", just dividends and social security, so no FICA due on those.