Yes. It would make sense for existing grocers unions to assist in the efforts of these Whole Foods workers, and eventually expand to Amazon Fulfillment workers (perhaps working with other unions under the AFL-CIO umbrella).

http://www.ufcw.org/grocery/

In the Seattle area, nearly every grocery store (except Whole Foods) employs workers represented by UFCW 21: https://www.ufcw21.org/shop-union

none of those exist in my part of the U.S. I haven't even heard of the last two