4. Types of employment. For the purpose of placing a ceiling over the fees charged by persons conducting employment agencies, types of employment shall be classified as follows:
Class "A"-domestics, household employees, unskilled or untrained manual workers and laborers, including agricultural workers;
Class "A1"-non-professional trained or skilled industrial workers or mechanics;
Class "B"-commercial, clerical, executive, administrative and professional employment, all employment outside the continental United States, and all other employment not included in classes "A", "A1", "C" and "D";
Class "C"-theatrical engagements;
Class "D"-nursing engagements as defined in article one hundred thirty-nine of the education law.