In a lawsuit, you could subpoena them to testify--they would be forced to come to court and testify (though, of course, it's possible they'd lie if they are sufficiently frightened for their jobs). I do not believe you can force them to testify at an appeal before certain administrative agenices--such as if you are appealing the denial of unemployment--though if you later appeal to the courts, you should be able to subpoena them at that point.