There is perhaps no shoe in the world more enduring than the Ugg boot. A style that takes cues from the surfers of Australia, the Deckers-owned Ugg brand is a billion-dollar enterprise that just never seems to go away.

When the sheepskin-lined booties debuted in the US in the mid-1980s, they were first considered footwear for the extreme outdoors enthusiast. But they exploded in popularity after the US Olympic team wore them in 1994, and then landed on Oprah’s Favorite Things list in 2000. Ugg boots became a fashion staple during the early aughts, worn by it-girls from Paris Hilton to Jessica Simpson, and have remained a cult-status item ever since. Even though the fashion world frequently turns up its nose at the boots, Uggs remain a best-selling, timeless classic.

But are they kosher?

This is a pressing question that is currently plaguing the Orthodox Jewish community. Because for all the popularity the boots enjoy for being warm, comfy, versatile, and reasonably affordable as far as investment pieces go, there has been recent concern that Uggs might violate a Jewish law: shatnez, or the biblical prohibition of wearing wool and linen together.

Following the rules of shatnez is a big deal in the religious Jewish community, to the point that there’s even a cottage industry of high-tech shatnez labs and checkers, who screen suits, jackets, and blankets to make sure the items don’t violate the rule. This week, according to the Five Towns Jewish Times, three different shatnez laboratories in New Jersey and England found shoes from Ugg that had both wool and linen in them.

These findings are causing a panic in the Jewish community (at least, judging by my Facebook feed and the WhatsApp chats I’m in with my ultra-Orthodox relatives and friends). This week alone, Ugg has reportedly fielded more than 500 queries from concerned Jews.

What is shatnez?

Shatnez is a Jewish law that has biblical roots. The law is written in the Torah, in Deuteronomy, chapter 22, verses 9 through 11: “You shall not sow your vineyard with two kinds of seed, lest the whole yield be forfeited, [a] crop that you have sown and the yield of the vineyard. You shall not plow with an ox and a donkey together. You shall not wear cloth of wool and linen mixed together.”

Jewish tradition ascribes plenty of reasons to its rules, and in this case, rabbinic understanding teaches that letting two different animals plow your field is cruel because they likely work at different paces and wouldn’t be able to keep up with one another.

But shatnez doesn’t really have an explanation behind it. It’s known as a chock, or law with an unspoken reasoning, and is supposed to be followed with blind faith.

To try to get some better explanation for shatnez, I called my father, a pious and deeply devout Jew who is definitely the smartest person on the planet (don’t argue with me on this). He’s highly knowledgeable about Jewish law and this was our conversation:

Hi, Daddy. Why do we keep shatnez? Because the Torah says so. But why does the Torah say so? Because it does. We don’t know why. Why is shatnez so important? Every law is important! But do I have to keep it if I don’t understand it? What??? Yes, of course. If everyone didn’t keep laws because they didn’t understand them, the world would be chaos!

As you can see, we didn’t get very far.

The TL;DR about shatnez is that wearing wool and linen together is a big no-no for observant Jews. When buying products that are wool or linen, like a coat or a suit, religious Jews may send their purchases to shatnez labs to make sure there’s no other material interwoven. While shoppers may assume clothing that is tagged as 100 percent linen or wool actually is, manufacturers will often use recycled materials under collars or in the lining.

Some shatnez laboratories say Ugg is mixing the two forbidden materials

Ugg is categorically denying that its shoes are made with both wool and linen.

In an email to me, Ugg senior service manager Mandi Geary says that the company has “been contacted by numerous members of the Jewish community following the release of erroneous information that our products contain both wool and linen. Please be assured that none of our current UGG® footwear products contain both wool and linen.”

But according to the Shatnez Test Center in Lakewood, New Jersey, seven different types of Ugg footwear styles were found to have wool and linen in them, including canvas sneakers, slip-on slides, moccasin slippers, and booties of the classic style.

The labs said some linen was used as a starched piece of lining under the Ugg tag, and another wool shoe was mixed with nylon even though it was labeled as a linen-cotton blend.

When one customer named Chaya reached out to Ugg customer service, according to the Jewish news site Yeshiva World News, a company rep wrote back that “all our products contain linen.” An Ugg company spokesperson reached out to YWN to clarify that the customer service rep was wrong, but this response has still triggered panic.

Shloime Fischer, a 70-year-old shatnez tester at the Shatnez Laboratory of Williamsburg who’s been in the business for 22 years, told me that since YWN published its story earlier this week, his phone has been ringing nonstop with inquiries from people all over the world, panicking that their Ugg shoes potentially contain shatnez.

“In all the years I’ve been working, I’ve never seen such a scare spread so fast,” he says. “It’s because of social media.”

Fischer says he’s checked Ugg boots in the past and has never found shatnez from the brand.

“Ugg is a big line, with tons and tons of shoes and boots, and it’s really not common for them to mix wool and linen,” he says. “It could be that some shoes have, but I would say that 90 percent of the shoes they make, especially the popular boots that everyone wears, don’t have shatnez.”

Can — and should — Jews wear their Uggs?

So what are religious Jews to do about their Uggs?

Several prominent rabbis have since ruled that the seven models the Shatnez Laboratory identified as containing wool and linen are forbidden to buy. (I reached out to Ugg’s internal team to find out if customers could get refunds to shoes that do have shatnez, and am waiting to hear back.) Some are vowing to stay away from the Ugg brand altogether.

Rabbi Dovid Feinstein, a prominent Torah scholar in New York City, has announced that it’s okay to wear the rest of Ugg’s footwear, since the brand is vehemently denying it does not mix wool and linen. Feinstein also says he’s waiting to hear back from more senior people at Ugg to get a full picture on how often the company mixes wool and linen.

Meanwhile, Rabbi Moshe Elefant, the COO and executive rabbinic coordinator at the Orthodox Union, told me that he thinks people should not be wearing Uggs until the company provides further information about its materials.

“I don’t think they really know all the facts yet, and it’s going to be hard to identify them because, unlike a dress or a suit, where shatnez experts know where to look, we are going to have to take apart an entire boot to check,” Elefant says. “And until we know for sure, I would advise people not to wear their Uggs.”

Yet others aren’t getting too worked up over it. Rabbi Adam Mintz, a Modern Orthodox rabbi from the Upper West Side congregation Rayim Ahuvim, called the situation “absolutely ridiculous.”

“I’ve never heard of people checking their shoes for shatnez,” he says. “If we’ve never heard of Ugg having shatnez, and the shatnez factory in Williamsburg says they’ve never seen shatnez in Uggs, why are they going and looking for it? People need to stop being so crazy about religion. Use good judgment.”

And some see the whole thing as comedic. Gav Bellino, the rabbi of the Sixth Street Community Synagogue in downtown Manhattan, who tells me he believes the Jewish community should “be spending our time worrying about much more important things,” posted a satirical letter to his synagogue’s Facebook page, making fun of the whole thing. Referring to the incident as the “Seven Deadly Uggs,” he told his synagogue members that they are not allowed to wear Uggs — not because they have shatnez, but because the boots are ugly.

“Uggs — even at the height of their popularity — were never fashionable or stylish,” Bellino wrote. “They do not provide height, encourage good posture, or even accentuate the leg. Why not just wear fur boxes on your feet? Did you actually need [the laws of] Shatnez to get you to stop wearing them? The trend was over before it began. In my humble opinion, they are a great blight on the entire footwear industry and should be banned from our holy synagogues and Torah institutions. May your piety in this manner and general good taste enhance our communities, further adorn the Crown of Torah, and elevate the [soul] of our teacher, Karl Lagerfeld.”