Former inmates at a privately-run Nashville jail say they were forced to work for free, making products for a business owned by the jail’s officials. The items, decorative plaques, “cornhole” lawn games, birdhouses and dog beds, made at the jail’s woodshop, were sold at a flea market and through a website, the Associated Press reports.

As proof, inmates Larry Stephney and Charles Brew wrote their names under fragments of wood nailed to the products, as well as the number “412148,” which is a section of the Tennessee code that prohibits jail authorities from profiting from inmate labor.

The company, Stand Firm Designs, now appears to have a defunct website, but the AP reported it previously stated it was a Christian firm “composed of retired contractors.” The inmates said they had to work sometimes long hours producing the items for the company, run by two current jail instructors and one former jail employee. The former inmates say the instructors took orders from guards and other officials in the jail. A batch of 25 birdhouses was said to be for one of the wardens.

The Nashville facility is run by the Corrections Corporation of America, the largest private prison company in the country, and it is now under investigation by the Tennessee Bureau of Investigation. Roy Napper, a former employee of the jail who helped operate the company told the AP the former inmates’ claims were untrue.