If Musk doesn't want his employees getting seduced by the Union, he should probably consider bumping the pay of his workers to near what the national average is and address any concerns they may have ( like excessive mandatory overtime per the article ). As long as he keeps his workforce happy, they'll have no reason to Unionize and Musk will have nothing to worry about.
Of course, there is the flip side.
Musk can say " screw this " and move the entire operation out of California and into another State where the cost of doing business is much lower.
"For every complex human problem, there is one and only one simple solution - and it is always wrong." - H. L. Menchken
First of all, Musk really can't increase Tesla workers' wages significantly. Tesla is still only marginally profitable, and, despite probably the most extensive use of industrial robots in the auto industry, it has a workforce of approximately 5,000 at the former NUMMI plant. A $10/hour raise for that many people (and this is assuming a 40-hour workweek with 10 holidays per year) would amount to an additional $10 million in wage costs per annum, plus additional payments to California and the U.S. for social security and other taxes. That's not peanuts. High wages for production line workers is one of the things that nearly killed the domestic auto industry by opening the door for less-expensive foreign imports from countries with lower labor costs (or more extensive automation - i.e.: Japan).
Secondly - and more cogently - Musk really can't move Tesla's manufacturing to another state. The deal he made to take over the NUMMI plant in Fremont is incredibly favorable to Tesla. He'd be really hard-pressed to find lower per-square-foot costs elsewhere, plus he'd have the expense of moving, re-installing, and troubleshooting the industrial robot army that produces and assembles most of each car. (Those 5,000 workers mostly do stuff like hook up wiring harnesses and so forth. There's essentially zero heavy lifiting involved in their jobs.) And then there'd be the six-to-twelve month halt in production while the changeover in facilities took place, just as Tesla is getting ready to roll out its first truly mass-production car, the Model 3. It's simply not a financiallyt realistic option.
In the parent article, Musk clearly states that Tesla has always been "union neutral". He's not anti-union. Nor is he pro-union. What he's against is the underhandedness of Jose Moran, who is essentially a union mole who took a job at Tesla specifically to agitate for a union vote. Apparently his mission was unsuccessful - Tesla's workforce was unreceptive to his message - so he quit his job (again, from the actual article, there is no current Tesla employee by that name) and has taken to tha Innerwebs to propagandize against Musk.
It's worth noting exactly why Tesla got such a sweetheart deal on the NUMMI plant: it's because astronomical labor costs made producinhg cars at the factory (which is ENORMOUS - Tesla occupies only a portion of the complex) unprofitable for GM and Toyota, the joint owners of NUMMI, so they SHUT IT DOWN in 2010, eliminating 4,700 jobs altogether.
That, I suspect, is why the UAW's mole found so little support among Tesla workers. Many of them are former NUMMI employees. They remember the good times and relatively high wages - but they also remember what happened to those good times and good wages when their former employer decided to shutter the plant because of those high wages