You've probably noticed labels on clothing you have purchased but may not have realized that an individual crafter is required by US government regulations to attach the same types of labels to handmade apparel items made by the crafter (which are for sale), the same as any large clothing manufacturer is required to do. Below are some links where you can get the information you need for complying with US labeling requirements when selling your handmade clothing (apparel) items.

Apparel Labeling Laws

Clothing: Fiber Content and Care Labels

US Labeling Laws Specifically Regarding Cotton
A label that states the fiber content must be attached to each clothing or household item that you are selling. The information at this link says that this includes clothing and accessories, draperies, floor coverings, furnishings, and beddings made from cotton fiber or cotton yarn.

Care Labeling of Textile Wearing Apparel and Certain Piece Goods as Amended

Wedding Gown Label Requirements - This link also tells about the fees for non-compliance. It's a lot!
Labeling Actions:
US vs Milady Bridals
Care Labeling Rule Cases and Fees For Noncompliance

This page from U.S. Code explains definitions used in the Textile Act and Rules. In regards to labeling laws for items made with yarn, it mentions knitting and goes on to say "or otherwise fabricating into a fabric".
http://www4.law.cornell.edu/uscode/15/70.html

Labeling Requirements under the Textile and Wool Acts

Rules and Regulations Under the Textile Fiber Products Identification Act

Regulations You Need to Know
When Making Stuffed Toys To Sell

If you're selling handmades, what you need to know About the USA Textiles Labeling Requirements on items that crafters make to sell.

Where to Get Labels (Care/Content, Size, Custom Printed)

URL of this page is
http://crochet.about.com/library/bllabel_apparel.htm