An advocacy group that says it is funded by undisclosed restaurants and food companies is taking advantage of the E. coli outbreak at some Chipotle Mexican Grill locations to again urge consumers to stay away.

In an ad in the New York Post on Wednesday, the Center for Consumer Freedom proclaimed in all-caps: "You Can't Spell 'Chipotle' Without E. Coli."

The ad mentions earlier Salmonella and norovirus outbreaks with ties to the chain, with copy such as, "But what really matters is if your high-calorie burrito will make you feel sick to your stomach."

Chipotle on Tuesday said it continued to work with health department officials after an E. coli outbreak was linked to eight of its restaurants in Oregon and Washington state. Washington state health officials said there were 25 reported cases as of Tuesday, while Oregon health officials knew of 12 cases of E. coli linked to eating at Chipotle restaurants around Portland, Ore.

The company has closed 43 locations, promising additional deep cleaning and sanitization at restaurants in the affected areas, environmental and food testing, and retaining two consulting firms to help it assess and improve its food safety standards.

Chipotle declined to comment on the latest ad from the Center for Consumer Freedom, which has been running its "Chubby Chipotle" campaign since early September, arguing that the chain's organic pitch doesn't mean its food is particularly healthy.

The group declined Wednesday to identify the sources of its funding beyond saying it receives contributions from restaurants, food and beverage companies, foundations and individuals.

In a statement Tuesday, Chipotle Chairman and Co-CEO Steve Ells said: "The safety of our customers and integrity of our food supply has always been our highest priority." He added that the company works with a number of very fresh ingredients. "If there are opportunities to do better, we will push ourselves to find them and enhance our already high standards for food safety. Our deepest sympathies go out to those who have been affected by this situation and it is our greatest priority to ensure the safety of all of the food we serve and maintain our customers' confidence in eating at Chipotle."

The outbreak was first reported over the weekend. Shares of Chipotle have fallen about 3.4% so far this week. The shares were trading at $618.67 in midday trading Wednesday on the New York Stock Exchange.