The sentence created using B does not make sense.
The court decision says that workers cannot be laid off if something. What is that something?
The sentence created using B basically seems to convey that that something is that they are given reason to believe that their jobs are safe. So let's get this straight. They can't be laid off if AT THE SAME TIME they are given reason to believe that their jobs are safe? That's what the present tense are given conveys, and that does not make sense.
Additionally, B does not make sense because the conditional would is used, but no condition for what would happen is mentioned. In other words, their jobs would still be safe if what? The answer to that question is not provided. If anything the sentence created using B seems to nonsensically convey that the workers cannot be laid off if they are given reason to believe that their jobs would still be safe even though they are being laid off.
What does make sense is, as the sentence created A conveys, that they cannot be laid off if ON AN ONGOING BASIS they have been given reason to believe that their jobs will be safe.
The present participle have been given makes sense, in that what is being conveyed is that on an ongoing basis the workers have been given reason to believe that their jobs will be safe.
So A is the best answer.