Hiring guidelines follow certain processes for good reason; they establish parameters for professional relationships between employers and new hires. Employers advance an offer letter outlining terms of employment, notes the Texas Workforce Commission. If the potential hire feels satisfied with the terms, she accepts the offer and its accompanying terms of employment.
Offer letters aren't the same thing as an employment contract, though, and offer letter amendment is possible, especially in an "at-will" position where employee or employer can terminate the agreement if it proves unsatisfactory. Read offer letters carefully, though, since certain words can help protect the initial terms.
Offer letters can contain contractual rights for new employees, although companies don't necessarily consider these documents to be employment contracts. If the offer letter clearly states you will receive a guaranteed bonus, but then you don't receive the bonus, this might be considered breach of contract. According to Arcoro, offer letters are considered to be less binding than employment contracts by courts, although states have different laws governing how these contracts are interpreted.