Whiteghyll Plastics employee Richard Perry and a colleague was covering roof lights with blackout vinyl to reduce the heat in the Bradford factory on June 2014. He fell through a fragile roof light into the fabrication department.
An investigation by the Health and Safety Executive (HSE) found the firm had opportunities to stop the pair from carrying out the job but neglected to supervise the work.
Andrea Jones, the HSE inspector overseeing the investigation said this lack of supervision led to Perry's death: "This accident would not have happened if these two employees had been appropriately supervised by management."
The company, which makes retail display materials, pleaded guilty to breaching Section 2(1) of the Health and Safety at Work Act (HSW Act) and was fined £120,000 and ordered to pay £37,655 in costs.