Whenever an action has been commenced in any court of the United States seeking relief from egregious or flagrant conditions which deprive persons residing in institutions of any rights, privileges, or immunities secured or protected by the Constitution or laws of the United States causing them to suffer grievous harm and the Attorney General has reasonable cause to believe that such deprivation is pursuant to a pattern or practice of resistance to the full enjoyment of such rights, privileges, or immunities, the Attorney General, for or in the name of the United States, may intervene in such action upon motion by the Attorney General.