SilverWook said:

IIRC, they took one of the original Chewie suits out of storage and recolored the fur for TPM.

There are conflicting reports on that. It's also been said that it was sculpted by John Coppinger for TPM. It certainly looks like it could be a repurposed Chewie costume but you have to wonder how well it would have held up after 15 years.

Edit: Scratch that, just looked up an old interview with Coppinger and in it he confirms it's a repurposed suit.

One of my best days in filmland was being in an original Wookiee suit for the voting scene in The Phantom Menace. It’s a powerful experience being ‘inside’ such an iconic character – grown men and women turn into little children when confronted by a Wookiee. And two years ago I finally got the chance to thank Peter Mayhew for not coming over to the UK to play the part!