With a valuation of $69 billion and a presence in almost every country, Uber has helped define what's become known as the gig economy, in which smartphone owners work as contractors rather than full-time employees. Uber advocates for the flexibility of this arrangement, saying drivers can set their own hours and work for as much or as little as they'd like. But governments and labor advocates around the world have challenged the company, saying it takes advantage of workers and doesn't offer them the rights typically afforded to official employees.