HONG KONG—Hong Kong's billionaires are used to being at the center of criticism over a widening wealth gap, but as the city's largest strike in nearly six years stretches on, the town's richest man, Li Ka-shing, is becoming a lightning rod for social inequality.

For nearly two weeks, hundreds of the city's dock workers have been on strike, crippling the world's third-busiest container port. The workers are demanding a 20% pay raise and better working conditions.

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