Can an employer decrease an employee's salary?

Texas follows the at-will employment doctrine.  This means that an employer can fire, promote, demote, transfer, change job duties, change work locations etc. of an employee at any time for any reason or no reason.  By the same token, the employee is free to quit anytime he or she desires. Two caveats to the above: 1) the employer cannot reduce pay for work already performed.  It can only do so into the future; and 2) the employer cannot discriminate against a worker on the basis of his age, sex, race, national origin, religion, color, disability, filing of a workers comp claim or refusing to commit a criminal act. Assuming both positions were at-will positions (ie you son had no contract in either), then most likely the employer was free to promote and demote your son and raise and lower his compensation for any reason or no reason at any time with or without notice. Otherwise, if you think there is more at issue, you should contact a Texas attorney in or near the county in which your son works or worked and preferably one who is Board Certified in Labor & Employment Law.