Demonstrators gather at a rally organized by Hugo Moyano, leader of CGT labor federation ahead of May Day celebrations in Buenos Aires, April 29, 2011. Argentine union boss Moyano has the power to bring the nation to a standstill. But the burly trucker is dreaming bigger, imagining a unionist in charge at the presidential palace. REUTERS/Marcos Brindicci (ARGENTINA - Tags: CIVIL UNREST POLITICS TRANSPORT)