Why did my female cat start peeing on my laundry?

I have had my female Calico cat for 4 years and she ALWAYS uses her litter box.  A month ago she peed in my laundry basket on my dirty clothes so I got a new basket with a lid.  Today, I was sorting my clothes, washed one load and when I returned for the second load she had peed on the pile of clothes I left on the floor to launder.  I've washed my clothes with vinegar which gets out the smell, but need help as to why she has started this behaviour.  It's not frequent, I was home with her today and she was acting normal.  

Is she peeing on the clothes because she smells the remnants of her last time?  She has a litter box and uses it, she's a good cat but I'm a frustrated owner.  Any recommendations other than not leaving the dirty laundry on the floor waiting to be washed?

Apparently cats weeing in places they shouldn't be might be a sign they're trying to tell you something. You should take her to the vet.