In the United States, the term 'chain migration' is used by advocates of limiting immigration, to partially explain the volume and national origins of legal immigration since 1965. U.S. citizens and Lawful Permanent Residents (or "Green card" holders) may petition for visas for their immediate relatives including their children, spouses, parents, or siblings. Advocates of immigration restriction believe the family reunification policy is too permissive, leads to higher than expected levels of immigration, and what they consider the wrong type of immigrants. In its place, they favor increasing the number of immigrants with particular job skills. In practice, however, the wait times from when a family reunification petition is filed until the adult relative is able to enter the U.S. can be as long as 15–20 years (as of 2006). This is a result of backlogs in obtaining a visa number and visa number quotas that only allow 226,000 family-based visas to be issued annually.