May I apply for a job if it will cause someone else to lose theirs?
One may not approach an employer directly and offer their services if it will result in a current employee being fired. This applies even to an employee who was recently hired and was about to begin working there.
However, one may accept a position if they are approached by an employer, even if they will be replacing a current employee. It is also permissible to advertise one’s availability and desirability to the general public, even if being hired results in someone else losing their job. Similarly, one may apply for the position of someone who is being let go, but only if the employee is being fired regardless.
For his part, an employer may not directly recruit a person working elsewhere, causing another employer to lose a worker.