Barring an employment contract (see below), this would be legal. Employees in your state without employment contacts are "employees at will." An employee at will may be fired at any time, for any reason--including for doing things which other employees do, or which this employee has done before; and since you could be fired at any time for any reason, the employer can take any steps "short of" termination, such as suspension, demotion, cutting pay, transfers, etc.(Note that so long as the employer is not discriminating on a protected basis--for example, not discriminating due to an employee's race, religion, age over 40, sex, or disability--the employer does NOT have to treat all employees equally or fairly; it can punish employee A for something B, C, and D also do.)If you do have an employment (including union) agreement, then its terms in regard to discipline and suspension will control--you could only be suspended in accordance with the contract.