MADISON, Ala. — Across the United States, mammoth corporations and family businesses share a complaint: a shortage of workers. As the unemployment rate has tunneled its way to a half-century low, employers insist they must scramble to lure applicants.

The shadow of age bias in hiring, though, is long. Tens of thousands of workers say that even with the right qualifications for a job, they are repeatedly turned away because they are over 50, or even 40, and considered too old.

The problem is getting more scrutiny after revelations that hundreds of employers shut out middle-aged and older Americans in their recruiting on Facebook, LinkedIn and other platforms. Those disclosures are supercharging a wave of litigation.

But as cases make their way to court, the legal road for proving age discrimination, always difficult, has only roughened. Recent decisions by federal appeals courts in Chicago and Atlanta have limited the reach of anti-discrimination protections and made it even harder for job applicants to win.

It is complicating an already challenging juncture of life. Workers over 50 — about 54 million Americans — are now facing much more precarious financial circumstances, a legacy of the recession.

More than half of workers over 50 lose longtime jobs before they are ready to retire, according to a recent analysis by the Urban Institute and ProPublica. Of those, nine out of 10 never recover their previous earning power. Some are able to find only piecemeal or gig work.

“If you lose your job at an older age, it’s really hard to get a new one,” said Richard Johnson, an Urban Institute economist who worked on the analysis.

‘The Look in Their Eyes’

Tom Adair dressed in a sharply pressed white shirt and a blue blazer with gold buttons for the weekly meeting for ExperiencePlus, a group for job seekers over 50 held in the small library at St. John the Baptist Church in Madison, Ala., near Huntsville.

A former quality manager at Toyota and an Air Force consultant, Mr. Adair said he has had temporary consulting assignments over the last decade but has not been able to get a steady full-time job since the recession’s nadir in 2009.

“I ace the phone interviews,” Mr. Adair said. “They say: ‘Your résumé speaks volumes. You could hit the ground running. It looks like you’re the perfect fit.’”

“But you come in, and you’re D.O.A.,” said Mr. Adair, who is 71 and has neatly clipped gray hair. “You can see the look in their eyes.”

“My wife says: ‘We need to get you a face-lift. We need to get your hair dyed,’” he said.

Older workers are much more likely to wrestle with prolonged joblessness than younger ones, according to the Bureau of Labor Statistics. On average, a 54-year-old job hunter will be unemployed for nearly a year.

Repeated inquiries can go unanswered, like space probes lost in a distant galaxy. In one of the most comprehensive studies, résumés were sent out on behalf of more than 40,000 fictitious applicants of different ages for thousands of low-skill jobs like janitors, administrative assistants and retail sales clerks in 12 cities. In general, the older they were, the fewer callbacks they got.

Those in their 60s “never do better, and often do worse,” than those a decade or two younger, said David Neumark, an economics professor at the University of California, Irvine, who oversaw the research.

It is toughest for women, who suffer more age discrimination than men starting in their 40s, the researchers found. “The evidence of age discrimination against women kind of pops