"Reasonable time" is not a requirement of an employer of an at will employee. The employer can act unreasonably, irrationally and with a mean spirit, and it would still be legal. Similarly, the employer can reduce the pay scale in any way it wants at any time it wants, for any reason, or for no reason at all, as long as the motivation is not an unlawful reason. Nothing in your post suggests an unlawful reason.
Unfortunately, you have few rights other than to leave the minute you decide you do not like the terms being offered.
Good luck to you.
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Unfortunately, employees and job applicants have very few employment rights, and employers have a lot of leeway in how they choose to run their businesses. In general, an employer can be unfair, obnoxious or bad at management. And an employer can make decisions based on faulty or inaccurate information. An employer has no obligation to warn an employee that he or she is not performing as the employer wants. It’s not a level playing field. An employer hires employees to provide work for its benefit, not for the benefit of the employees. Don't expect the employer to take care of its employees; it doesn’t have to and it rarely does.
There are some limitations on what an employer can do, mostly in the areas of public policy (such as discrimination law or whistle blowing), contract law, union-employer labor relations, and constitutional due process for government employees. Please see my guide to at-will employment in California which should help you understand employment rights: http://www.avvo.com/legal-guides/ugc/an-overview-of-at-will-employment-all-states. After you take a look at the guide, you may be able to identify actions or behavior that fits one of the categories that allows for legal action. If so, an experienced plaintiffs employment attorney may be helpful.
Employment rights come from the state and federal legislatures. One of the best things people can do to improve their employment rights is vote for candidates with a good record on pro-employee, anti-corporate legislation. Another way to protect employment rights is to form or affiliate with a union, or participate in a union already in place.
I hope you can resolve your situation and wish you the best.
@MikaSpencer * * * twitter.com/MikaSpencer * * * PLEASE READ: All legal actions have time limits, called statutes of limitation. If you miss the deadline for filing your claim, you will lose the opportunity to pursue your case. Please consult with an experienced employment attorney as soon as possible to better preserve your rights. * * * Marilynn Mika Spencer provides information on Avvo as a service to the public, primarily when general information may be of assistance. Avvo is not an appropriate forum for an in-depth response or a detailed analysis. These comments are for information only and should not be considered legal advice. Legal advice must pertain to specific, detailed facts. * * * No attorney-client relationship is created based on this information exchange. * * * Marilynn Mika Spencer is licensed to practice law before all state and federal courts in California and can appear before administrative agencies throughout the country. She is eligible to represent clients in other states on a pro hac vice basis.