If a former supervisor badmouths you to potential employers during your job search, it could hinder your job prospects for years to come. Although you might never know that’s the reason you can’t get hired, if you do suspect a former boss is speaking ill of you, you’ll need to do some investigating to prove his actions and take steps to restore your professional reputation.

Ask Employers

Some employers will offer feedback regarding their decision not to hire you. If you suspect a previous boss is giving you a bad reference, ask employers if your last supervisor’s opinion played a role in their decision to turn you down. They might not be willing to tell you exactly what he said, but they might give some indication that his review was less than favorable. For example, if he had only good things to say about you they’ll probably tell you but if they’re vague about his answer, that’s a good indicator that the conversation didn’t go well.

Enlist Professional Help

You can hire a professional reference-checking service to contact your references and prior employers and determine if they’re giving you a negative review. These services don’t disclose they’re working on your behalf, so they can ensure that they get the same recommendation employers are receiving. Some services offer a transcript of the call, including direct quotes, tone of voice or other signals your boss sends. In most cases you’ll receive a report within about a week, though some providers offer a “rush service” for an added fee.

Check Your Own References

If you don’t want to pay to check your references, you can always do it on your own. It's best not to make the call yourself because your boss will likely recognize your voice. Enlist a friend, family member or colleague to contact your supervisor and ask for a reference. Have them pay close attention not only to your supervisor’s words, but also his tone of voice. In some cases, his words might not be overtly critical, but he might use a sarcastic or hesitant tone that implies he has a low opinion of you.

Speak to Your Former Boss

You can also go straight to the source. Your boss might not tell you the truth if you contact him directly, especially if he’s maliciously attempting to block your job search. However, he might provide clues that he gave an unfavorable review if he knows you're onto him, even if he doesn't share exactly what he said about you. He might also admit to it if he feels justified speaking negatively of you. The key to approaching your boss is to avoid getting emotional or accusatory. Instead, calmly tell him you’ve had a hard time landing a job and would like to know what he’s telling prospective employers who contact him.