I'm not aware of any statutory law in Massachusetts regarding random drug testing of employees.  However, the Supreme Judicial Court of Massachusetts has held that such testing may violate the state's privacy statute (MGL, chapter 214, Section 1B) unless there are safety issues that make the drug testing necessary or the employer has some other "legitimate business interest" in the testing. (See, e.g., Webster v. Motorola, Inc. 637 N.E.2d 203 (1994)).

The example that is often given for "safety sensitive" positions is where the employee operates dangerous equipment.  I'm going to guess that, in your case, operating a front-end loader would qualify.  Examples of other legitimate business reasons for random testing might be where the employee works in a job with national security implications or where he has access to valuable proprietary information.  Hope that helps.  Follow this link for a discussion of other employee rights in MA.