From a supply chain perspective, the so-called “card check” law may be the biggest impact from the results of tomorrow’s presidential election.

As we’ve reported on these pages, the Democratic-controlled congress, propelled by support from the major unions, wants to pass legislation that would overturn the process dating back in the US to the 1800s that requires a majority of workers to approve unionization in a “secret ballot.”

That today means no one can know for sure how a given employee voted. They could outwardly appear supportive of a unionization drive, but vote No in the privacy of the election place.

Under the card check law, a union could be formed if a majority of workers signs a pro-union ballot or “card” during a given period. That means union officials will know who has signed up and who hasn’t – and apply pressure to any workers not joining the cause.

Home Depot founder Bernie Marcus has called it a “path to economic ruin.” (See Is Potential New Union Rule a “Path to Economic Ruin?”)

As I said in an earlier First Thoughts column, I believe this is a real Pandora’s Box that may bring changes no one can really foresee now. The percent of workers currently in unions continues to fall, especially those workers outside of government. Unions obviously would like to reverse that trend, and see the card check as a powerful – and perhaps rapid – way to do that.

The law still faces challenges. Obama would have to win in order to ensure no presidential veto of a Congressional bill, and if Republicans hold on to at least 41 Senate seats, they may be able to filibuster the thing to death. But, this really is at the top of labor’s agenda, and they no doubt would feel they deserve some pay back for helping the Democrats regain control of the Congress in 2006 and maybe also the presidency in 2008.

What will it mean? No one can know how fast and where such unionization efforts would go. My own hunch is it would start slow for a variety of reasons, but then accelerate as union officials figured out the best approaches to guarantee success in the card check campaigns.

Will Wal-Mart at long last be unionized? What would the resulting impact on costs have for its growth and market share? Would union efforts in manufacturing lead to more offshoring and automation, killing the jobs unions hoped to bolster? Would it strengthen the working class in a way that is good for the whole economy? Are unionized companies actually hoping the law passes to even the playing field against non-union competitors? Will more business uproot to right-to-work states? Will China increase its worldwide market share?

No one knows. That’s what’s scary. If there was some way to do a “pilot program,” that would sound a whole lot better to me.

I’d love your thoughts on this.