Labor cost are not high in any way shape or form, unless you are comparing cost to slave labor in China or Vietnam.
1968 labor cost was 34% of overhead for US Manufacturing.
Today 2017 labor was 3% of overhead for manufacturing.( might be 2016, it has been 4 years since I took that class).
The dollar in 1968 is not the same as today.
That's a disingenuous comparison.
In 1968 manufacturing was incredibly labor intensive with very little automation. The same with the entire supply chain that went into producing those manufactured items. The amount of human labor required to manufacture one unit was at least an order of magnitude greater than it is today (in reality it is multiple orders of magnitude in most fields).
Manufacturing today is a high precision undertaking that generally uses a lot of automated systems that are very capital intensive but have relatively low operating costs. So while labor today takes up a much smaller percentage of the per unit cost of a manufactured good the profit margins on those manufactured goods have not substantially improved.
Take the UAW strikes. If the auto makers give in then they will go out of business. If they try to eat the increased labor costs then they tank profit margins to basically nothing and become unable to fund future R&D and production out of free cash flow and instead have to borrow at relatively high interest rates, they also tank their stock price. The other option is to pass the price increases onto the consumer as higher automotive prices; except one of the biggest limiters currently on new car sales is how expensive new cars are. All increased prices will do is tank market share and in turn reduce profitability still further.
That is especially true when compared to other auto manufacturers. Take Tesla. They are locating more and more of their business in Texas which lets them avoid state income taxes (unlike the Big 3), they aren't unionized and so can get away with a much more agile (and cheaper) labor force, and one of their biggest R&D spends is on figuring out how to replace ever more of their manufacturing work force with robots.
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Fundamentally, unions are broken in the US and Canada. Frankly, they are parasites on both the corporations and their membership. What unions should do is offer their own retirement and health plans along with becoming something akin to employment agencies. So that a company can go to the Union and say "We need X number of workers with Y skills for Z period of time. How big a check do we have to cut you to get that work force?" and then the union provides the work force. The company gets to off load responsibility for retirement, benefits, recruitment, and a lot of HR issues onto the union while the union gets to focus on providing the benefits that its members actually desire.
But what the UAW is doing right now? It's straight up extortion. In a sane world the Big 3 would be able to just say "Fine, you don't want to work for us? Ok. You are all no longer employed and we are now advertising to fill your previous slots on these terms. And by the way, everyone who went on strike is ineligible for rehire with us."