"The purpose of the law label is to inform the consumer of the hidden contents, or “filling materials” inside bedding & furniture products. The law label was born in the early 1900s to prevent these articles from being further manufactured with contents such as horse hair, corn husks and whatever else a manufacturer could find to use that the consumer would never see, similar to food labeling." from http://en.wikipedia.org/wiki/Law_label
If it's your mattress you can. But if it's not your mattress or if you are a merchant selling them for other people to use is where the law comes in. Once the consumer makes the purchase they can remove the label.
It is merely a warning label. If it is yours, and you do not plan on reselling it, then there is nothing wrong with removing it. Be warned that ripping it out breaks the strings that hold it together, and leads to your mattress unraveling. Cutting them often leaves a rough feeling edge. With that in mind I would suggest removing them only if the seeing them when changing the sheets drives you insane.