Yes, your employer can ask to see your texts, unless doing so violates the terms of a union agreement or employment contract. The fact is that most work relationships are "at will" which means that a company can set the conditions of the workplace much as it sees fit. That having been said, you can't be physically forced to turn them over; you can refuse. However, if you do so, you can lose your job. In fact, you can be fired for any reason or no reason at all, woith or without notice.