There is a known payout Minhag in Mosdos for compensation of one month per year of employment to an employee who is leaving a job. Our question is divided into two:
1. Does this Minhag have a Chiyuv or even a source in Halacha, like לא תשלחנו חינם or is it just a type of gratitude?
2. Does it apply to everyone or only to a specific field of employment or to a certain age of the employee or their wealth circumstances.
1. There are two aspects. Paying out one month per year is based on local common custom. This forms part of the actual salary as per common employment custom.
An independent issue is the concept of Haanaka (הענקה) based on ethical considerations.
ראה חינוך מצוה תפב. לקו״ש יט ע׳ 155. (ושקו״ט אם הוא בגדר שכר פעולה או לא, ראה בלקו״ש שם. וש״נ. וראה עוד ענין בהענקה בלקו״ש כד ע׳ 87. ואכ״מ)
2. This depends on the established local common practice. Recently, a book was published dedicated entirely to this topic by the name חודש לשנה.
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