The AP has it:

A lunchtime parade of topless porn stars down the main street of New Zealand’s biggest city has been given official approval, as no laws will be broken.
The parade later this month will feature up to 30 porn stars riding on the back of motorcycles or in open cars through Auckland’s CBD to promote an erotica exposition.

Usually when there’s a topless march, it’s in support of some cause like Greenpeace, Cancer Research, Focus on the Family (not so fast, Dobson). That’s all well and good, but it’s nice to see the straight-forward literalism of showing boobs to promote the further showing of more boobs.