Taco Bell was recently sued because its meat only contains 35% beef, with the rest being fillers such as water, wheat oats, soy lecithin, maltodrextrin, anti-dusting agent, and modified corn starch.  The suit wants them to discontinue using the word "beef" because it doesn't meet federal standards.

More information can be found at Taco Bell defends lawsuit claiming beef doesn't meet federal standards with major ad campaign and this article at Fox News.