Ruby’s managing partner Tim Sykes didn’t realize quite how popular the Impossible Burger was until he couldn’t get it. When his usual distributor US Foods ran out of cases of the faux meat known for its realistic ability to “bleed,” Sykes went to other suppliers, to no avail. He asked his friends at the Flower Shop and Dudley’s, two New York City restaurants that also serve the vegan meat; they, too, were out of stock with no leads. “[It’s] super frustrating,” Sykes says. “I’ve never had a product where I can’t get it anywhere.”

Rather than completely remove the vegetarian burger option from Ruby’s two New York City locations, Sykes replaced Impossible’s fake meat with a version from its competitor Beyond Meat. But Ruby’s customers weren’t into the switch. “A number of people” came to order an Impossible Burger, Sykes says. When informed of the Beyond Meat replacement, they turned around and left.

Impossible Foods is having a big year. In January, the vegan meat company released a new and improved version of its beef substitute, the Impossible Burger 2.0, and in recent months, it announced that it was making major inroads into the fast-food market with deals with Qdoba, Red Robin, and Burger King. The latter deal was hailed as a potential industry game changer, a sign that the startup meat could go fully mainstream; just today, after a successful test run in St. Louis, Missouri, Burger King announced it will put an Impossible Whopper in more than 7,000 locations across the U.S. And now, all that expansion has led to some growing pains, and a shortage: Some restaurants are reporting that they’re unable to secure their usual cases of Impossible meat.

Earlier this month, Impossible reached out to distributors and, according to a spokesperson, “as many restaurants as possible” to let them know that an Impossible shortage was entirely possible. In a letter sent to distributors dated April 10, about one week after Impossible announced its partnership with Burger King, Impossible Foods explained that demand was outpacing the company’s manufacturing capabilities. It went on to say that given the demand, “we may not be able to meet the requested quantities amongst some of our valued partners in the short term.” The shortage was predicted to last through mid May.

Chris Caron, general manager of New York City vegan cafe Delice & Sarrasin, says he hasn’t run out of his Impossible product yet, but he prepared for the possibility. “We bought extra stock because the supplier told us they wouldn’t have enough for a while,” he says. “When I said I would order three cases, she said, ‘I only have two cases left for all of New York.’” Delice & Sarrasin uses the Impossible meat for just one dish, its tournedos rossini, typically a French steak dish, made here with Impossible Foods’ ground meat. The two extra cases Caron ordered from his distributor has meant Delice & Sarrasin will have enough to last through the shortage — he hopes.

After learning that his customers didn’t consider Beyond Meat a suitable replacement for the Impossible Burger, Sykes got lucky. In the middle of last week, he found a distributor with 11 cases of Impossible Burger. He bought them all, “the last 11 cases in America,” he muses. It will be just enough product to supply the two Ruby’s cafes through the mid-May mark.

The scramble for product is particularly frustrating for independent restaurant managers because Impossible Foods has long depended on independent restaurants for its growth. The first restaurant to sell an Impossible Burger was David Chang’s Nishi in NYC. The burger earned culinary credibility there and at higher-end restaurants like Traci Des Jardins’s Jardiniere in San Francisco before moving into casual chains and, more recently, massive fast-food brands. It’s now in 7,000 restaurants worldwide, an Impossible Foods spokesperson tells Eater. In Asia, Impossible Foods sales have tripled. Much of this growth has occurred in just the past few months — and that’s not counting Impossible’s direct-to-consumer potential, as it won’t be available in grocery stores until later this year.

The company is working to ramp up production to meet the new demand. Impossible Foods is increasing the hours of operation and number of employees at its plant in Oakland, California, which currently operates in two shifts on a single production line. Impossible Foods is in the midst of hiring for a third shift and by summer, the company expects to have a second production line up and running, doubling production. The company is also “actively pursuing strategies for adding “more manufacturing capacity,” a spokesperson said, but they declined to go into detail on those plans.

In the meantime, restaurants must figure out how to fill customer demand for the popular vegan meat. Brooklyn vegan cheese shop and cafe Riverdel ran out of Impossible meat last week. The shop usually gets four cases of Impossible per week and manager Christhina Verna says Riverdel often sells out of its Impossible-made burger. When she got a call from Impossible Foods alerting her to the shortage, she says she didn’t think much of it. “At that time I didn’t think we were going to have a problem getting it, so I was just like, ‘Oh cool, thanks. Bye.’ And then I [thought] I should have asked more questions,” she says.

Verna believes Riverdel will secure more Impossible product soon. If it doesn’t work out, she’s not worried about having to drop the vegan burger from the menu. Like Ruby’s, Riverdel could switch to Beyond for a bit. “I’m sure it’ll be fine,” she says. “We’ll survive.”

But, replacing the one-of-a-kind Impossible Burger isn’t actually so simple. “We can normally source something creatively but it’s nationwide,” Sykes says of the shortage. Plus, as he recently learned, “I guess vegans and vegetarians are loyal to certain brands.”