Bill Ackman just took a massive stake in Chipotle and wants to shake things up (CMG)

Bill Ackman wants to shake things up at Chipotle.In a regulatory filing on Tuesday, his hedge fundPershing Square disclosed a 9.9% stake in the fast-food chain, and said it is seeking talks with the company.Shares of Chipotle jumped following the news.Ackman's stake makes him the second-largest shareholder in the company."The Reporting Persons [Pershing Square] believe that the Issuers Common Stock is undervalued and is an attractive investment," the 13D filing stated.A13D filing is typically used when aninvestor takes an activist stance to demand changes. These can range from increased dividends or share buybacks to management shakeups.Ackman intends to enter discussions with Chipotle's management on the company's business, operations, cost structure, assets, and others, according to the filing.Pershing Square has targeted companies ranging from JC Penney to Canadian Pacific Railway.He took an activist short position in Herbalife in 2012 betting the shares would decline whilealleging that the company operated like a pyramid scheme.Chipotle has fought to win customers back since outbreaks of E. coli and norovirus were linked to its restaurants late last year.The company'sshares jumpedby as much as 8% in after-hours trading. Theyslid 42% in the year through Tuesday's market close, slammed by investors' concerns about food safety.Chipotlereported its first quarterly loss ever in April, and has used a loyalty program and free foodto try and lure customers back."We welcome their investment, and appreciate the confidence theyve expressed in our brand, differentiated offering, visionary leadership and strong growth opportunities," said Chris Arnold, Chipotle's spokesman, in a statement to Business Insider. The company only learned of Pershing Square's investment on Tuesday, Arnold said.Pershing Square declined to comment.(With assistance from Rachael Levy and Hayley Peterson)SEE ALSO:Get ready for the 'return of volatility'DON'T MISS:Chipotle tweets about sex and marijuana in desperate attempt to win back millennialsJoin the conversation about this storyNOW WATCH: You can now get a burrito out of a vending machine ' and it's surprisingly tasty
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