Richard C. Shelley, a truck driver for Port East Transfer Inc. near Baltimore, vented his frustration about his job in a time-honored manner: He wrote graffiti on the men's room wall.

For his work-place penmanship, Shelley got fired.

Shelley's graffiti bad-mouthed company owner and president Edwin Hale Sr. for forcing five of 40 truckers to submit to urine testing for drug use, which Shelley called "a witch hunt." To protect truckers from testing, he wrote, "We need a union."

Hale -- who usually used another restroom -- learned of the graffiti, obtained writing samples of his drivers, determined Shelley to be the culprit and fired him. But the matter did not end there.

The case of Port East Transfer and Richard C. Shelley entered the annals of U.S. labor law on Feb. 28 with a unanimous 3-to-0 ruling by the National Labor Relations Board that Shelley's firing was illegal. The NLRB, upholding a 15-page decision by an administrative law judge, said Shelley must be reinstated in his job with back pay. The company is considering an appeal.

The graffiti incident in Rosedale, Md., is the most recent in a long list of work-place cases involving the conflict between a worker's right of free expression and an employer's right to maintain decorum and protect himself and his staff from criticism, according to labor law experts.

"I couldn't say openly that we need a union. Drivers knew Hale was against a union and you'd be fired," Shelley, 24, said in an interview. "So they fired me for what I wrote, and I just didn't think that was right. People were afraid of talking about unions."

Employes can be fired -- and often have been -- for angering the boss orally or in writing, according to past NLRB rulings, which include work place graffiti cases ranging from angry written tirades to obscene cartoons.

But when these statements or writings become a form of union activity, the worker can be protected on the grounds that discussing whether to form a labor union is a "protected activity" under the National Labor Relations Act -- even when that discussion occurs on a restroom wall.

The Port East graffiti case was complicated because the key evidence was destroyed. Hale was so angry that shortly after Shelley's firing May 14 he ordered the wall painted, according to his lawyer, Warren M. Davison.

Hale declined to discuss the case. But Davison said it was the reference to a "witch hunt," rather than the call for a union, that angered the company president. "The writing about the union was a minor part, and not the reason for terminating," he said.

But NLRB Judge Mary Ellen R. Benard, who heard the case last August, and the board, which reviewed her decision, disagreed. Benard cited the testimony of Hale's son, Edwin Jr., who said his father explained Shelley's firing by saying: "You have to cut people out . . . who are union organizers . . . out like a cancer. Because it'll kill your business."

Port East had a union election in 1981, when drivers overwhelmingly rejected joining the Teamsters. Hale Sr. had made clear he "strongly opposed" unions, Benard said.

If Shelley's graffiti had not focused on the union, his firing likely would have been legal, experts said. "There's no First Amendment right for employes' free speech" to protect them from being fired, "but there is some protection under labor law," said Lawrence Z. Lorber, a Washington management lawyer who specializes in cases involving firing.

"You can say the boss is a expletive deleted and hold him up to ridicule, and you are usually not protected by law," Lorber said. "But if you say the boss is a expletive deleted , and we need a union to fight him, then you may possibly be protected."

In the Port East restroom, according to Benard's ruling, there was already graffiti about Hale, including an obscene cartoon of him, when Shelley added his writing. Benard said the content of the graffiti "was not so malicious, defamatory, insubordinate, obnoxious and wholly unjustified" to merit firing.

"The judge found it was common to write graffiti, and the only time a guy gets disciplined is when he writes about the union," said NLRB regional director Louis D'Amico. "It's like if people are talking on the shop floor about football pools. Then someone talks about the union -- and gets fired for talking."

Shelley, who had passed the drug test, now works for another nonunion firm and said he is happier in his new job. He said his father, a union member, encouraged him to take his case to the NLRB. "I'm glad I did it," he said. "I'm not in this for the money. I want workers to know they have a right to organize a union."