“The requirements for classification as an H-1B nonimmigrant professional may or may not include a license because States have different rules in this area. If a State permits aliens to enter the United States as a visitor to take a licensing exam, then USCIS will generally require a license before they will approve the H-1B petition. However, some States do not permit aliens to take licensing exams until they enter the United States in H-1B status and obtain a social security number. Therefore, a visa should not be denied based solely on the fact that the applicant does not already hold a license to practice in the United States.”

Source: http://www.state.gov/documents/organization/87226.pdf