Forcing people who are injured to apply for Social Security before paying their claims appears to bolster insurers’ profits in several ways. If claimants refuse to apply, the insurers can simply stop paying their benefits, said Dawn Barrett, an employee of the Cigna Corporation, who grew frustrated sending people to Social Security and who is now a plaintiff in one of the lawsuits. More typically, she said, people apply for Social Security when an insurer tells them to. That allows the insurer to reduce its claim reserves, money that is kept in conservative investments for benefit payments. And in the insurance industry, smaller reserves mean bigger profits.

Image Jessica Ortiz of San Diego said her disability insurer called more than 10 times after she was hurt in a car crash, insisting that she apply for Social Security. She was denied, as she had expected. Credit... Sandy Huffaker for The New York Times

“It’s all about the numbers,” Ms. Barrett said.

Finally, disability insurers tell many of their claimants to appeal Social Security’s rejections again and again, until some are finally accepted. Then the insurers can take those people off their rolls, shifting the cost to the government.

Whistle-blowers have filed lawsuits against the Unum Group, America’s largest disability insurer, and Cigna, another large one, though there is no dispute that the Social Security requirement is an industrywide practice. Unum, with revenue of $10.5 billion, paid disability claims of $4 billion last year.

Both companies said their claims practices were fair, legal and consumer-friendly.

“Our goal is to ensure that each member receives all of the benefits to which he or she is entitled,” said Jill Roman, a spokeswoman for Cigna.

The lawsuits do not fault the idea of coordinating benefits with Social Security and workers’ compensation. Instead, they contend that insurers are recklessly dumping people on Social Security’s doorstep, without properly screening them to make sure they have a chance of qualifying.

The typical long-term disability policy says workers can collect when they are unable to do their own jobs for some period, usually more than five months. Social Security, by contrast, will pay only those people who are so badly disabled they cannot do any job at all. The disability must be one that will last more than 12 months or that will lead to death within that time.

Mr. Sabourin, the spokesman for Unum, denies the suits’ accusations and says that his company does screen people. He said Unum considered it in the best interests of its claimants to try for Social Security, because the federal program offers advantages over private insurance. Even though the federal requirements are tough, he said, Social Security has certain exceptions and trial programs that Unum’s claimants might qualify for.