I see offer letters that make a specific job offer and then say, by the way, this isn't a contract. Guess what? Offer plus acceptance equals contract. I don't care what that disclaimer says, it's still a contract.
Now, what the contract means is another thing. It may say you're at-will, which means they can fire you for any reason or no reason at all. Some states have exceptions to the at-will doctrine. In all states, at-will still doesn't affect your rights under discrimination and whistleblower laws.
Your offer letter probably has your starting position and salary listed. That means the employer is bound by this once you accept. If you're at-will, they can change it, but luring you in with a promise of a management position and high pay and then making you a minimum wage janitor is not only a breach of contract, but is likely fraud.
The offer letter probably also lists benefits and other terms. You are bound by the terms, as is your employer.
Of course, if you sign a more detailed agreement when you start, then the offer letter may be no longer in effect. Most contracts say they supersede all prior contracts. Be careful to read what you sign, especially that giant pile of papers they give you when you start. Don't sign something you can't live with.
If it turns out that the employer had no intention of living up to its deal when it made the offer, such as offering a nonexistent job or benefits, then you could have fraud claims along with your breach of contract claims.
So make sure to keep a copy of that job offer. If it's an email, print it and keep it. Keep anything you sign. It may be a contract, and it might come in handy later. It might also contain post-employment obligations you have to comply with such as a noncompete agreement.
If there's something you don't understand in the offer, make sure you get clarification before you accept. Offer plus acceptance equals contract. If the company is bound, so are you. Pay attention to what you are agreeing. If you don't understand it, get legal advice from an employee-side employment lawyer before you accept.
Have a general question about employment law? Want to share a story? I welcome all comments and questions. I can't give legal advice here about specific situations but will be glad to discuss general issues and try to point you in the right direction. If you need legal advice, contact an employment lawyer in your state. Remember, anything you post here will be seen publicly, and I will comment publicly on it. It will not be confidential. Govern yourself accordingly. If you want to communicate with me confidentially as Donna Ballman, Florida lawyer rather than as Donna Ballman, blogger, my firm's website is here.