That is a bunch of crap!!!
Based on the figures in that article, if taxing $80 billion in union dues would return $25 billion in tax revenue, that would mean that the average tax rate paid by those union workers would be over 31%. Exactly how many union workers do you honestly think makes enough money so that the rate on their taxable income is 31%?
Based on 2010 federal tax tables, a married couple would have to have had taxable income (this is after all the deductions were taken) of something over $200,000 before they would be paying a tax rate that high. Even a single person would have to have taxable income of over $170,000. Now can you honestly tell me that the AVERAGE (because that is what it would have to be to achieve the figures quoted in what you posted) taxable income of all the union dues-paying Americans was over $170,00 - $200,000 per year? I DON'T THINK SO!!!!!