America is running out of Impossible Burgers

New York(CNN Business) There's real demand for fake meat.

Interest in Impossible Foods' plant-based meat alternative is growing so much that the company is struggling to keep up, the company said Tuesday.

The acknowledgment comes just after the company expanded its partnership with Burger King. Earlier this week, the fast food chain shared that it plans to sell the meatless patty as a Whopper at all of its US locations by the end of the year. Restaurant Brands International, which owns Burger King, said a St. Louis test of the Impossible Whopper went "exceedingly well."

That nationwide rollout would essentially double the amount of restaurants that Impossible works with. Burger King had about 7,300 locations nationwide at the close of last year. Right now, Impossible supplies its product to about 7,000 restaurants.

On top of that, demand for Impossible products within those 7,000 locations has more than doubled, Impossible Foods CFO David Lee told CNN Business.

The company also said it's been stretched thin because of growth from "every sales category where Impossible Foods does business," including small restaurants, other chains, like White Castle, and attractions, like theme parks and college campuses.

In a statement, Impossible said that it "recognizes the inconvenience that this shortage is causing and sincerely apologizes to all customers, particularly those who have come to depend on the additional foot traffic and revenue that the Impossible Burger has generated."

Impossible added that it is not facing a shortage of the ingredients it uses to make the plant-based meat. "We are facing short-term ramp-up challenges resulting from demand greatly outstripping supply," it said.

To keep up with demand, Impossible is increasing the number of hours its Oakland, California, plant is open. It's also hiring for a planned third shift. And it is installing a second production line that the company says "should double current capacity."

Lee said he is confident that Impossible will ultimately be able to meet the demand. The company is "not sparing any expense" to keep up, Lee told CNN Business. "We absolutely will continue fundraising."

Until the shortage is resolved, Impossible is encouraging its fans to call ahead to see if their restaurant has the meat in stock.