See the following section copied from:http://union.okstate.edu/iss/EmploymentTax/12monthOPT.htm
EMPLOYMENT ALLOWED WHILE ON OPT
All OPT employment must be in a job that is related to the student’s degree program. This employment may include:
• Paid employment – Students may work part-time (20 hours per week) or full-time
• Multiple employers – Students may work for more than one employer, but all employment must be in the student’s degree program
• Short-term multiple employers – performing artists – Students must keep a list of gigs, the dates and duration.
• Work of hire- 1099 employment which an individual performs a service based on contractual relationship. Students must be a list of contract periods and the name and address of the contracting company.
• Self-employed business owner – Students on OPT may start a business and be self-employed. Student must work full-time and be able to prove the proper business licenses and engaged in business related to student’s degree program.
• Employment through an agency – Students must provide evidence from the employer that the student worked at least 20 hours per week during the period of employment.
• Unpaid employment – Student may work as volunteers or unpaid interns. The position must be at least 20 hours a week and it is suggested that you obtain a letter from the employer for evidence of the volunteering.