The growth of the disability rolls has accelerated since the recession hit in 2007. As the labor market tightened, workers with disabilities that employers previously accommodated on the job — painful hips, mental disorders, weak hearts — were often the first to go. Finding new work often proved difficult, causing many to turn to the disability rolls for support.

The migration of so many people from work to the disability rolls is raising concern among lawmakers in Congress that the program is being stretched beyond its original intent of providing a safety net for former workers whose medical problems make them unable to work.

Last week, the Government Accountability Office found that the program made $1.3 billion in potentially improper payments to people who had jobs when they were supposedly disabled. The allegedly improper payments represent less than 1 percent of disability payments.

While fraud remains a concern, policymakers say the program’s biggest vulnerability is the subjective criteria that create a large gray area for applicants. A worker with physical impairments that are difficult to document precisely, like a bad back, can tolerate the condition while on the job but claim it as a reason to go on disability if he falls out of work for a prolonged period.