Those activists hollering and blocking traffic this week in Pittsburgh and other cities demanding $15 an hour for fast-food restaurant employees should remember the cautionary tale of AT&T Longlines. A strike in 1983 might seem like ancient history, but some lessons learned in that 22-day standoff still apply 33 years later.

Long before the advent of cellular telephone service, AT&T Longlines controlled 95 percent of long-distance telephone communications across the United States, plus all of the international calls into and out of the country. AT&T Longlines was a division of the company founded by the telephone’s inventor, Alexander Graham Bell, in 1885. Its 700,000 operators, linemen, sales clerks and secretaries maintained a network of wires, coaxial cables and microwave relay towers to provide nationwide service of near-monopoly proportion.

Those employees were represented by labor unions, chiefly the Communications Workers of America. CWA and two other unions declared a nationwide strike against AT&T Longlines in 1983, demanding better pay and reversal of health benefit “take backs” the company sought in contract negotiations.

While one of the central ideas of a labor strike is to punish a company by interrupting its business, AT&T suffered little. In the years leading up to the dispute, the company had quietly automated most of its maintenance and service operations — and the work that still required hands and eyes could be performed easily by a middle management force that by then had been made mostly redundant, also by the introduction of new technology. The ranks of middle managers remained faithful to the company rather than the union laborers, fearful that their own jobs might be on the line as well.

The employees suddenly were confronted with an immutable economic truth: In a free market, you’re paid the salary you command. The union leaders miscalculated, believing a strike could shut down AT&T Longlines in the summer of 1983. Service wasn’t interrupted in the least, and the value of the work force plummeted as a result.

That’s ultimately where this current, union-backed “Fight for Fifteen” will end — another shipwreck of good intentions.

Just last month, McDonald’s announced a nationwide roll-out of touch-screen self-service kiosks. Employees who once would have managed a cash register will now monitor a customer’s choices at an iPad-style kiosk. And you can bet it will be a much smaller workforce.

Other fast food chains are likely to follow McDonalds’ lead with self-service if the Fight for Fifteen continues.

That’s the company’s apparent position, according to a guest post published Wednesday on Forbes.com by Ed Rensi, former president and CEO of McDonald’s USA.

“It brings me no joy to write these words,” Rensi writes. “The push for a $15 starter wage has negatively impacted the career prospects of employees who were just getting started in the workforce while extinguishing the businesses that employed them.

McDonald’s has always taken pride in providing a first-job experience for many teenagers: a decent wage — not a living wage — for youngsters who are willing to work, willing to learn, and willing to leave childish, selfish attitudes outside the workplace.