My employer has been deducting 401(k) from my pay check each week, and neglecting to send it into the TPA who handles our retirement fund. They also neglected to tell us employees about it. Is this legal?

My employer has been deducting 401(k) from my pay check each week, and neglecting to send it into the TPA who handles our retirement fund. They also neglected to tell us employees about it. Is this legal?