"If you find yourself as an Herbalife employee today, my advice is that you should leave the company because this is not going to be a good thing on your resume. I'd go find another job," the Pershing Square Capital Management CEO said on CNBC's "Fast Money: Halftime Report." Ackman took his short position in Herbalife more than three years ago, and he said Monday his bet against the company is roughly $1 billion. He has publicly crusaded against Herbalife, repeatedly calling it a pyramid scheme and saying its business model harms people. His actions have not prevented Herbalife shares from climbing. The stock has risen more than 40 percent in the last year.