A T-shirt featuring bathroom humor may have made for a good gag gift, but to the legal department at Anheuser-Busch, it's not a laughing matter.

The beer giant sent a letter Monday to a small Blacksburg biotechnology company that produced the T-shirt, claiming that it represented a trademark infringement.

The T-shirt in question depicts a doctor, a nurse and a bare-bottomed patient. The nurse is holding a tray with a beer bottle on it and a frosty mug of beer in her hand. The caption has the doctor, who is pointing at the patient, saying, "I said a Butt Light."

"That one we never sold, but gastroenterologists love it," said Tracy Wilkins, president of TechLab. "It makes a great gag gift."

Selling T-shirts is not a profit-making venture for TechLab. Mostly, the company gives the shirts away to clients. But for $15, plus shipping, anyone can purchase one online.

The company, which was founded in 1989, is dedicated to the study of anaerobic organisms.

Specifically, TechLab develops, manufactures and sells intestinal diagnostics worldwide that focus on intestinal inflammation, antibiotic-associated diarrhea and parasitology.

Wilkins said they have about 15 different T-shirts designs that add humor to a business that works with feces on a daily basis.

"We are a poop business. We have to have a sense of humor," Wilkins said. "It's sort of sixth-grade humor."

The company's slogan is "No. 1 in the No. 2 business."

The letter from Anheuser-Busch said, despite the humor, the T-shirt was an infringement on its trademark.

"There can be no question that the Infringing Design is meant to call to mind BUD LIGHT beer," reads a part of the letter. "And even though you may have intended the design and message to be humorous, your actions nevertheless constitute trademark infringement and dilution in violation of federal and state law."

Anheuser-Busch asked that the T-shirt design be removed from TechLab's Web site, that the T-shirts with the depiction not be sold or distributed and that TechLab never use imitations of any Anheuser-Busch trademark or slogan in the future.

"Anheuser-Busch protects all of its trademarks from misuse by anyone who attempts to trade on the value of its famous brands," said Frank Hellwig, senior associate general counsel for Anheuser-Busch, in a statement. "Anheuser-Busch owes it to its shareholders to protect key company assets, its iconic trademarks."

Wilkins said he will comply, although he will give away a few more shirts. The T-shirt is no longer on the company's Web site.

"We're sending back a letter saying we will cease and desist and we are including some of the T-shirts," he said.

Sarah Wiant, a professor of law at Washington and Lee University who teaches courses on intellectual property including trademarks, said TechLab's T-shirt is likely not a violation.

Wiant said large companies like Anheuser-Busch vigorously enforce their trademarks, in part, because the law says that they must protect their marks or they risk losing them.

"In this particular instance, they are, as you say, poop people and are referring to the butt," she said. "Even if the image is absolutely identifiable to the Anheuser-Busch trademark logo, arguably it would be acceptable because it is a parody."

Often, however, Wiant said smaller companies do not fight larger corporations because of the time, energy and money required.

"I would argue that this little company probably has a very strong claim of defense -- but sometimes big companies browbeat others," she said.

Wilkins said, while he considered the fun he could have with the publicity, he didn't have the resources to fight.

"This is what big business does; at the same time, you can't afford to go up against them," Wilkins said. "We're only drinking Millers now."