Get it in writing. This piece of advice has as its implicit assumption that it is the written word and not oral proclamations which carry greater legal weight. Jewish law interestingly, posits that what we say is much more important than what we write. This should not be surprising when one considers that our tradition is meant to be an oral one handed down from teacher to student - it was only due to persecution and dispersion that we were even allowed to put to writing our laws and traditions. The great importance that Judaism places on proper use of speech eschewing all forms of "harmless" gossip and insisting on clean language is a reflection of this emphasis on the spoken word. While there may also be historical reasons for this - until the invention of the printing press obtaining accurate records was exceedingly difficult - psychologically, saying something has more of an impact than putting it in writing. It is for this reason that Jewish law insists that we orally confess our sins on Yom Kippur. It is not quite good enough to write a letter of apology to one you have wronged; you must call them or better yet go visit them to personally state your remorse. The fact that this is so difficult for most serves to demonstrate the effect of the spoken word.
Strictly speaking only oral testimony is acceptable in a court of law. Written affidavits can never be used to gain a conviction in a criminal case. Tone, demeanor, infliction and the like can not be put into writing. Thus with minor exceptions, the get (divorce document) being the most notable, written documentation is no more than a record of oral commitments. Nonetheless lest friction and misunderstanding ensue Jewish ethics strongly advises that all agreements be put in writing. Jewish ethical teachings frown on loaning money without documenting the terms in writing and signed by witnesses.
Absent oral or written testimony Jewish law follows local custom. In Talmudic times it was customary for the employer to provide lunch and even the menu served was subject to local practice. Thus an employee was within his legal right to demand steak over hamburgers if such was the norm at other places of local employment. Today when most people in the business world do not have written contracts - something that Jewish teachings would suggest is not a good idea - it is crucial to accurately determine local customs. With so many different 'work cultures' this is no easy task and at best can only help in providing some general guidelines. This information would theoretically establish proper guidelines in areas such as the appropriate amount of overtime, health and pension benefits, vacation pay and personal days. Absent a fully functioning beit din system it would prove difficult today for an employee to enforce his (Jewish) legal rights, nevertheless it does provide employers guidelines for proper treatment of their workers.
It is in areas such as health benefits or vacation pay that we see application of the principle that in civil law custom often supersedes Jewish law. Jewish law asserted that one gets paid only for worked performed. It has no concept of paid sick leave not to mention vacation pay. Why should an employer bear the burden of these costs? If a sick person has no means of financial support then society as a whole must bear the burden of care and if he does have financial resources surely the employer should not be forced to pay for work not received. Nonetheless modern day custom and thus Jewish law is that these are costs to be borne by the employer.