Finding the right employee used to be the most difficult aspect of the hiring process. Making the offer itself was simple: You just dropped a letter in the mail.

Now, however, that friendly letter welcoming the new employee on board may be considered a binding contract, and interpreted in ways the employer never anticipated. Courts across the country have held, for example, that if a salary is stated as an annual amount, the employee cannot be fired for a year. Or, if the letter says that the employee's performance will be reviewed in six months, then it is a contract to keep him or her on that long.

Joseph E. O'Leary, a lawyer with Choate, Hall & Stewart in Boston, advises his clients to include the employee's starting date, job title, salary, and benefits in an offer letter. But he suggests that salary should always be given in monthly terms. And instead of explicit statements about the timing of evaluations or raises, the letter should say, "Your performance and salary will be reviewed periodically." Also, O'Leary says, benefits should not be downgraded, even if company policy changes, unless the letter states that perks are subject to modification.

Some employers, in their concern over court interpretations of offer letters, have gone so far as to include such statements as "This letter does not constitute a specific term of employment," or, "This letter constitutes the entire agreement between us, and overrides any statements made during the interview process." But most lawyers advise against including harsh legalese, because, O'Leary says, "Language like this is so off-putting to the potential employee."