The union at Kenya's main port of Mombasa on Friday called off a strike after its management issued letters of employment to casual workers at east Africa's main trade gateway who were demanding permanent jobs.Simon Sang, secretary general of the dock workers union told workers the dispute had been resolved after most of their employment letters were signed, and the rest would be ready shortly."Go to your departments, all letters have been dispatched to the departments, pick your letter and go back to work," he said