Firms are being urged to end the "archaic" recruitment practice of asking job candidates to tick a box if they have a criminal record.
A survey by Business in the Community showed that most prisoners wanted to work after serving their sentence, but only a third would apply for a job with a tick box.
The charity said the tick boxes were excluding former offenders and served no purpose for employers.
Its campaign has already been supported by dozens of employers with a combined workforce of almost 400,000, but the charity said more companies should stop including the tick box on application forms.
Faye Goldman, campaign manager for Business in the Community said: "This research clearly shows that the tick box is an archaic recruitment practice which serves no purpose for either candidates or employers.
"Employment allows people to move on from their past and reduces re-offending rates, but many of the prisoners we surveyed perceived the tick box to be a major barrier, despite having qualifications and a desire to work.
"Feedback showed that many of the prisoners want be open and honest with employers but don't feel confident they would be given a fair chance if they were."
Business in the Community surveyed over 120 prisoners at Nottingham Prison.