UPDATE 1-S.Korea truckers vow fuel strike, president under fire

(Adds result of truckers' union vote, details)

By Jon Herskovitz

SEOUL, June 9 (Reuters) - South Korean truckers voted on Monday to strike over high oil prices, piling more pressure on the export-dependent country's new president whose policies have sparked mass street protests.

Lee Myung-bak has seen his support nosedive after only 100 days in office due to simmering anger over a U.S. beef import deal, jeopardising his business-friendly economic reform plans.

The truckers' union added to the negative sentiment with a majority of its members voting on Monday to stop work unless the government introduced new countermeasures to cope with soaring diesel prices.

Lee is bracing for one of his toughest weeks in office with a major street protest planned for Tuesday and a transport strike looming.

In a bid to win back public support, he is expected to announce within days a cabinet reshuffle.

"This is a critical juncture," said Lee Nae-young, a professor of political science at Korea University.

During the race for the presidency, Lee's strength was his can-do image, first fostered when he ran Hyundai Construction and enhanced when he transformed Seoul as its mayor.