It was inevitable that the merger of heavily unionized Northwest Airlines and mostly nonunion Delta Air Lines would encounter some labor turbulence.

Less predictable was that organized labor would try to use the merger -- and the election of President Obama -- to challenge the spirit of the 83-year-old Railway Labor Act, which was amended in 1936 to cover airlines. Organized labor argues that the National Mediation Board should change what unions call outdated and unfair election rules to make it more likely labor will come out on top. Delta and other carriers are fighting the request, arguing that there's no compelling reason to alter rules that have covered railroads and airlines for decades despite numerous challenges.

The companies make the stronger argument. The case has important implications for all carriers, large and small, and their employees.

Most U.S. businesses are covered by labor laws that require a union only to win a majority of the votes cast to organize workers. But the National Mediation Board -- the agency created under the Railway Labor Act -- established more difficult rules for unions seeking to organize transportation workers. The aim was to minimize economic upheaval from strikes because of the vital role of transportation companies in interstate commerce. In railroad and airline elections, employees who don't vote are counted as "no" votes, so unions have to win a full majority.

Delta uses the example of 10,000 ramp workers. Under current rules, 5,001 of those workers would have to vote for union certification. But under the request the AFL-CIO filed with the mediation board in September, if 1,000 ramp workers actually voted in the election, only 501 votes would be needed to certify a union covering 10,000 employees.

The example is especially apt because the Mediation Board is holding up elections on 10,000 ramp workers and 20,000 flight attendants at Delta while it considers the AFL-CIO request. It's all part of an expected clash of cultures at Delta, where about 15 percent of workers were represented by unions before the merger with Northwest. About 95 percent of Northwest's employees were unionized before the merger, but they make up only about one-third of total employment at the combined carrier.

It's clear labor expects the Mediation Board to be more sympathetic to its causes under the Obama administration, which recently appointed a former airline union leader to the board to take the place of a former Northwest lobbyist. There are now two former union leaders on the three-person board. But the argument over election rules shouldn't turn on pro- or anti-union leanings.

The same interstate commerce issues that were in play when the rules were adopted remain relevant today. The two-week pilots' strike at Northwest in 1998 was a local taste of the economic disruption an airline shutdown can create. Imagine a similar situation at Delta, which became the world's largest carrier in the merger.

It's also important to note that nothing in the rules prevents unions from successfully organizing. In fact, dozens of unions have won certification votes at railways and airlines despite the more challenging voting rules.

Each time the election rules have been challenged before, the Mediation Board has stayed the decades-old course. Nothing has changed to justify altering that flight plan in 2009.