A person’s immigration status can change quickly. People who entered the U.S. legally with a temporary work or student visa may find their status changed to undocumented if they remain in the U.S. after the visa has expired. In such cases, the status changes with no affirmative action on the part of the visa holders.
In other cases, people may take steps to change their immigration status. Someone with conditional permanent residence status, for instance, may file a petition to remove the conditions of residence (Form I-751 or I-829) after fulfilling the requirements. Since conditional permanent residents receive a green card valid for only two years, if they fail to take the necessary steps to have the condition removed, they lose their legal resident status and become undocumented.