The Department of Justice and two civil rights groups filed lawsuits to block an Iowa immigration law that would allow local law enforcement to arrest and detain immigrants who have been previously deported or denied entry to the US. It also gives judges the power to order that someone be returned to the country they entered from. The DOJ lawsuit says the law is unconstitutional and that immigration regulation is the federal government's responsibility. Supporters argue the law is needed to enforce immigration laws, while critics say it oversteps authority and could target legal residents.