• Motif asked the U.S. Patent and Trademark Office to revoke a patent held by Impossible protecting the company's heme technology.
• Impossible sued Motif in March, claiming that the start-up's heme-based beef alternative too closely imitates its own version.
• Both companies are privately owned, although Impossible is much larger, with a valuation of $9.5 billion.

Plant-based meat maker Impossible Foods could be at risk of losing a key patent as part of an ongoing legal dispute with competitor Motif FoodWorks.

Motif asked the U.S. Patent and Trademark Office to revoke a patent held by Impossible protecting the company's heme technology. Impossible sued Motif in March, claiming that the start-up's heme-based beef alternative too closely imitates its own version.

Impossible's beef and pork substitutes use soy leghemoglobin, which is produced from genetically modified yeast, to imitate the taste and aroma of real meat.

Both companies are privately owned, although Impossible is much larger, with a valuation of $9.5 billion. Along with publicly traded Beyond Meat, Impossible has helped rejuvenate the market for vegetarian burgers. Losing its patent on heme could mean even stiffer competition within the meat alternative market.

Motif filed a petition with the USPTO's Patent Trial and Appeal Board on Wednesday to ask a panel of judges to review Impossible's patent and weigh whether it should be revoked.

"We are confident the Patent Trial and Appeal Board will agree with our view that the patent never should have been issued and revoke it," a Motif spokesperson said in a statement to CNBC. "Our industry should work together to grow the plant-based category for the greater good — to benefit people and the planet. Competition is healthy. And it should play out in the marketplace, not the courts."

An Impossible spokesperson told CNBC in a statement the company is confident in the strength of its patent and that its expects to prevail in court and before the patent office.

"Motif's stunt is a baseless and meritless attempt to distract from the fact that they have infringed on our patent and are unlawfully using our technology to build their business," the spokesperson said.

Motif has raised $343.5 million from investors including Bill Gates and was valued at $1.23 billion last year, according to Pitchbook. It was spun out of biotech start-up Ginkgo Bioworks.

When Motif launched in 2019, Ginkgo co-founder and CEO Jason Kelly told CNBC that Impossible's success inspired the formation of Motif, which develops key ingredients for making plant-based proteins and leaves the rest to food companies.

Impossible alleges that Motif's Hemami product infringes on its patent for a beef replica using heme, a molecule found in traditional beef burgers that Impossible and Motif both use as an ingredient. Motif's version uses bovine myoglobin as its heme source.

In its original complaint, Impossible said its patent covers the invention of a beef substitute that uses a muscle replica including a heme-containing protein, at least one sugar compound and one sulfur compound. It also protects against the invention of a meat alternative that mimics meat through a fat tissue replica that uses at least one plant oil and a denatured plant protein.