EXCLUSIVE

Octomom Nadya Suleman is under the microscope after a complaint was lodged that she committed welfare fraud ... and if it's true Octo could go to prison.

TMZ has learned ... someone made the allegation last week to the L.A. County Dept. of Welfare Fraud Prevention and Investigation (WFP&I), claiming Octo is getting various forms of welfare, including food stamps, even though she made nearly $200,000 in 2012.

Under California law, Octo can legitimately collect welfare for her and her 14 kids if she makes $119,000 or less in a calendar year, but if the allegation is true ... she exceeded the limit by a lot.

Law enforcement sources tell us ... the WFP&I is conducting a probe and has already interviewed witnesses in Octo's world.

If WFP&I determines Octo committed welfare fraud, she can be prosecuted. If convicted she could face more than 3 years in prison.