The answer depends on your employer's policies and reason for searching. When courts evaluate workplace privacy claims, they balance the employer's legitimate justification for intruding against the employee's reasonable expectation of privacy. If something of great value to the company has been stolen that day, and the employer decides to search all employees in a reasonable way (for example, searching their bags, not their bodies), then your employer has a pretty good reason to search. Particularly if your employer has a written policy warning employees that they might be subject to search, which diminishes employees' expectations of privacy, this type of search might be legal. However, an employer who does this as a daily routine, targets you specifically without a good reason, or searches more intrusively, will be on shakier legal ground. This is especially so if the employer has no policy on searches and has not conducted searches in the past, which makes your reasonable expectations of privacy stronger.
For more on how courts evaluate workplace privacy claims, see Nolo's article Proving Your Privacy Was Violated at Work.