Rayon does indeed shrink and one of the reasons they combine it with other fabrics now. Spandex is not known for shrinking however when blended with other fabrics that will shrink (cotton, linen, rayon, tencel) there is a potential for shrinkage. Rayon (by itself) is recommended to be dry cleaned only....
Funny thing is that polyester does not shrink, but combine it with rayon in a hot washer/dryer and it will!
*~"Never eat more than you can lift......" Miss Piggy~*