With four million members in the United States and Canada, Sean McGarvey, president of the building and construction trades unit of the mighty AFL-CIO, is the type of Keystone XL pipeline backer the U.S. president cannot ignore.

Trade unions such as the American Federation of Labour and Congress of Industrial Organizations — the United States’ largest union federation — had a big hand in Barack Obama’s re-election, much like the environmental movement that opposes the Alberta-to-Texas oil sands pipeline.

And their patience with the anti-XL camp is wearing thin.

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