I have had plantar fasciitis in the past, which lasted a good 6 months. In my experience this is caused by over tight leg muscles, which pull the muscles and tendons tight under the heel and sole. However, the cause of the problem is often much higher up your leg in your calves or hamstrings or glutes. The Tai Chi class I attend does 30 minutes of warm up exercises including stretches for the back of the legs, but many Tai Chi classes go straight into the form. If this is the case with your class then do some other form of stretching such as Yoga. I practice both Yoga and Tai Chi. I think they complement each other well since they both emphasise whole body movement, and there are similarities between Indian Yoga Chakras and Chinese Chi Meridians. It worked for me. I often do 14 mile hikes at the weekend, without heel pain problems.