The INS requires 90 days to grant employment authorization. If you are obtaining permanent resident status based upon a relative rather than a job, you must have both an approved immigrant visa petition and a current priority date. There is an exception to this rule, however, for the spouses of permanent residents and the unmarried children of permanent residents under 21 who have been waiting for more than three years for their immigrant visa. It sounds like something important. Your priority date can be very important, and the priority date concept requires some explanation.
Backlogs result when the demand for a category exceeds the number of green cards available.
Each month the Department of State publishes a Visa Bulletin which lists those priority dates which are current. Your priority date must be current, which means that an immigrant visa is available to you, in order to file for adjustment of status and employment authorization. Except for persons born in China and India, most employment-based preferences are current. There is a long wait for immigrant visas under the other worker category. Except for the spouses and unmarried children of United States citizens, there is a significant wait for immigrant visas in all family-based preferences for every country in the world.