Foreign students are typically funded the same way as domestic (US) students, although federally subsidized student and parent loans and work-study assistance are generally limited to US citizens and nationals, permanent residents, and approved refugees. Moreover, some funding sources (such as many NSF fellowships) may only be awarded to domestic students. Other factors contributing to possible financial difficulties include high costs to visit their families back home, supporting one's family who is not allowed to work due to immigration laws, tuition that is steep by world standards, and large fees: visa fees by US Citizenship and Immigration Services, surveillance fees (such as Student and Exchange Visitor Information Systems, or SEVIS) by the United States Congress and the United States Department of Homeland Security.