The above cbs news article is from national review online, so you will need to check the source, the labor relations institute or whatever it is sighted in the article, I can't see the exact name from this post page, so just look up there to get the exact source.
Another source of information on union political donations:
http://www.unionfacts.com/articles/unionPolitics.cfm
In 1992, the Teamsters reportedly gave a massive amount of political money to the presidential candidate it knew its membership did not support. According to author Duke Zeller, "As for the actual amount of Teamster money poured into the Clinton-Gore campaign, Gene Giacumbo, a former elected member of [former Teamsters president Ron] Carey's board, believes the total figure to be even higher. 'Carey himself bragged to me that the union gave $56 million to Clinton,' he confirmed, 'and this was after an independent, outside poll the union paid for showed the membership responses preferred Perot, then Bush, with Clinton in third place.'"
Another source of information on union political donations:
http://www.unionfacts.com/articles/unionPolitics.cfm
In 1992, the Teamsters reportedly gave a massive amount of political money to the presidential candidate it knew its membership did not support. According to author Duke Zeller, "As for the actual amount of Teamster money poured into the Clinton-Gore campaign, Gene Giacumbo, a former elected member of [former Teamsters president Ron] Carey's board, believes the total figure to be even higher. 'Carey himself bragged to me that the union gave $56 million to Clinton,' he confirmed, 'and this was after an independent, outside poll the union paid for showed the membership responses preferred Perot, then Bush, with Clinton in third place.'"