Chipotle stopped serving pork at nearly one third of their restaurants in the U.S. after a supplier violated the company’s standards and was suspended. The company stopped serving the topping for bowls and burritos, according to The Associated Press.

Chris Arnold, spokesman for Chipotle, said that they were notified Friday about the supplier’s violation through an ordinary audit. The timeline for when pork, or carnitas, will reappear in the hundreds of locations again is unknown. Arnold said that it is difficult to know how long the shortage will last.

Arnold said that the violations came from the way that pigs were being housed. Chipotle is strict on their pigs being raised by suppliers who keep them in humane conditions with access to the outdoors. Crowded pens are not acceptable.

The Human Society of the United States Vice President of Farm Animal Protection Paul Shapiro claimed that most pigs being bred in the U.S. stay on concrete floors in gestation crates. He said that most pigs that end up in the pork industry do not have access to the outdoors or proper bedding.

Shapiro added that access to the outdoors varies even at farms where conditions are much better than those described. He said that this does not mean animals are living in good conditions on “Old MacDonald’s farm.” And he hopes that the issues concerning Chipotle’s current supplier will be resolved.

Customers may have seen signs on other occasions stating that a restaurant is serving meat that doesn’t meet a company’s standards. These may have described the meat as not being raised responsibly. Arnold said that Chipotle has had difficulties landing beef with no hormones or antibiotics. The company proceeds to serve beef described as being raised conventionally.

However, that is not the case for carnitas. Arnold stated in an email that a substitution like this one is not going to be made. Arnold stated that Chipotle is investigating several different options to repair the shortage of pork. They are exploring increasing orders from different suppliers and tossing around ideas concerning uses of other cuts of pork.

As of Sept. 30, Chipotle Mexican Grill Inc. had nearly 1,800 U.S. restaurants. The restaurant chain has had strong sales growth in the past. Part of this has to do with their ability to market their food as a higher quality than other fast-food restaurants, according to AP.

Stephen Anderson, Miller Tabak analyst, credited Chipotle’s management for stopping the selling of pork that did not meet their ethical standards, but he added that the loss of carnitas will have an effect on sales numbers in the future. He said that about 7 percent of customers order pork, and although some will substitute it for other items on the menu, at least 2 percent will go elsewhere. Shares of Chipotle fell rapidly and hit as low as 700 Wednesday.

Chipotle is not the only chain to experience issues with their ingredients. In November, Buffalo Wild Wings had to raise the prices on their menu due to the rising costs of chicken wings. Beef prices have compressed margins for several restaurants operators from McDonalds to Ruth’s Hospitality Group as well.