SANAA  - Saudi Arabia has begun deporting thousands of Yemeni labourers following new regulations requiring foreigners to work only for their sponsors, a Yemeni official said on Monday, a move that could "significantly damage" the poor country's economy. Some two million of Yemen's 25 million citizens work abroad, more than half of them in larger and richer neighbour Saudi Arabia. Remittances bring in $2 billion a year to Yemen, a country still grappling with revolt, a separatist movement and an Islamist insurgency. "If the decision is implemented, it will cause significant damage to the ... Yemeni economy, of which expatriates are a backbone since their remittances reach about $2 billion a year," adviser to Yemen's PM, told Reuters.