For most organizations, an activity is an unrelated business (and subject to unrelated business income tax) if it meets three requirements: It is a trade or business, It is regularly carried on, and It is not substantially related to furthering the exempt purpose of the organization. More

Unrelated Business Income Resources
Technical Information Release 06-7 
Statutory Changes Relating to unrelated Business Income of Nonprofit Corporations
830 Code of Massachusetts Regulations (CMR) 63.38T.1 
Taxation of Unrelated Business Income of Exempt Organizations