Chipotle Mexican Grill appears to be taking another swing at Panera Bread.
A week after Chipotle disclosed that it had revamped its tortillas to be additive-free, the Mexican chain released an online game called "Spot the Imposter."
The game asks customers to pick between Chipotle's preservative-free ingredients and "industrial additives." They are rewarded with mobile coupons for free orders of chips and guacamole and a chance to win other food prizes.
The company has launched several online games in the past, but this one appears to be a dig at competitor Panera, which Chipotle has criticized for using natural additives in its menu items.
"At Chipotle, our real ingredients have nothing to hide," Mark Crumpacker, Chipotle's chief marketing and development officer, said in a statement announcing the promotion. "Other restaurants are trying to make their ingredients sound better by switching artificial colors, flavors and preservatives for friendlier sounding additives that serve the same purpose."
However, when asked about the comment by CNBC, Chipotle spokesman Chris Arnold said, "We have not singled out Panera or any individual restaurant company. This is a move that is occurring across the category."
"This isn't about Panera, it is about an industry that has been focused on removing artificial additives and replacing them with "natural" counterparts, which are often synthesized in the same way as artificial versions and have nothing to do with the ingredient they replace," he continued. "Take 'natural beef flavor,' for example, which is often used in fast food french fries. While it is 'natural,' and contains nothing artificial, it is generally synthesized from plants and has nothing at all to do with beef."
Chipotle is on a quest to woo back customers it lost after a series of high-profile foodborne illnesses. With the outbreaks behind it, Chipotle is working to restoring its image, which was built on the freshness of its ingredients.
This image is important because it is a trait valued by certain diners, especially millennial moms who tend to seek out healthier fare.
Last week, when Chipotle said it had succeeded in ditching additives from its entire menu (excluding beverages), the company noted the distinctions between its "clean" claim and that of its competitors like Panera and McDonald's.
It's too soon to say if Panera will strike back. But on Friday, when asked about Chipotle's recent jabs, Panera CEO Ron Shaich told CNBC he was friendly with Chipotle CEO Steve Ells and had worked with him in the past.
Chipotle shares were trading up 1.6 percent, while Panera shares gained 7.6 percent on speculation of a potential takeover of the company.