<Table> <Tr> <Th> National Football League labor relations </Th> </Tr> <Tr> <Td> <Ul> <Li> 1982 strike </Li> <Li> 1987 strike </Li> <Li> 2011 lockout </Li> <Li> 2012 referee lockout </Li> <Li> Collective Bargaining Agreement </Li> </Ul> </Td> </Tr> <Tr> <Td> American football portal </Td> </Tr> <Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> </Table> <Tr> <Th> National Football League labor relations </Th> </Tr>

When did the nfl referees go on strike