A group of unions and advocacy groups filed a lawsuit on Tuesday seeking to block the Trump administration from enforcing new visa restrictions that would limit how long foreign students and journalists can stay in the U.S. without applying for extensions.The Department of Homeland Security's rule creates fixed periods of admission for people in F status as international students, J status as exchange visitors and I status as foreign journalists.People in those classifications generally have been admitted for the duration of their studies, exchange programs or qualifying media assignments rath...