“Not for profit corporation” means a corporation organized under the General Not For Profit Corporation Act of 1986 that is not dominant in its field and employs fewer than 50 full-time employees or has gross annual sales of less than $4,000,000. For purposes of a specific rule, an agency may define a not for profit corporation to include employment of 50 or more persons if it finds that such a definition is necessary to adapt the rule to the needs and problems of not for profit corporations.