An upcoming GAO report obtained by NBC News says the federal government may have paid $1.29 billion in Social Security disability benefits to 36,000 people who had too much income from work to qualify.

At least one recipient collected a potential overpayment of $90,000 without being caught by the Social Security Administration, according to the report, which will be released Sunday, while others collected $57,000 and $74,000.

The GAO also said its estimate of "potentially improper" payments, which was based on comparing federal wage data to Disability Insurance rolls between 2010 and 2013, "likely understated" the scope of the problem, but that an exact number could not be determined without case by case investigations.

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To qualify for disability, recipients must show that they have a physical or mental impairment that prevents gainful employment and is either terminal or expected to last more than a year. Once approved, the average monthly payment to a recipient is just under $1,000.

(Read more: Social Security Benefits—10 Things You Must Know)

There is a five-month waiting period during which monthly income cannot exceed $1,000 before an applicant can qualify for disability, as well as a nine-month trial period during which someone who is already receiving benefits can return to work without terminating his or her disability payments.