So apparently PETA is okay with people wearing fabrics in which animals were killed in the Alberta Tar Sands to make oil to make petrochemical products.
Remember anything containing nylon, polyester, rayon or so called "synthetic materials" means animals were killed during the process.
Tar Sands = Oil = Petrochemicals = Polyester Shirt = Dead Animals killed by the Tar Sands
So basically what PETA is saying is "It is okay to wear clothing that indirectly killed animals, just so long as you are not directly killing animals and wearing those animals skin or fur or wool."
Learn more by reading Fashion Accessories for Vegans.