Yes, but there could be legal consequences, so an attorney's advice should always be sought before rescinding the offer.
Even if an employer has stated on all offers that employment is at will and can be terminated at any time, there is the concept of the employer making a "promise" of a job. If the promise of a job is rescinded, it could cause economic and emotional harm to the candidate. For example, the candidate could end up jobless because he or she has given notice at the current job; the candidate may have incurred relocation costs; or he or she may suffer emotional distress.
Promissory estoppel is a legal doctrine that supports a harmed party in enforcing such promises made, even if a true contract did not exist. Many candidates have successfully used this argument to win their cases in court, and some have used additional arguments connected to breach of the implied covenant of good faith and fair dealing, fraud and misrepresentation, and reckless, negligent or intentional misinterpretation and infliction of emotional distress.
When an employment contract itself actually exists and was signed by the parties, breach of contract can be added to that list of claims, and an employer could easily find itself on the losing end of such a battle.
In all cases, regardless of whether the employer feels the candidate suffered losses, a complete legal review of the situation should be conducted. It should include interviews with all employees who spoke with the candidate and may have inadvertently made promises to that person. The offer should then be rescinded only with the approval of legal counsel.
An organization run by AI is not a futuristic concept. Such technology is already a part of many workplaces and will continue to shape the labor market and HR. Here's how employers and employees can successfully manage generative AI and other AI-powered systems.