In this case the union is telling the truth

in the Politico:
AFL to White House: 'Labor isn't an arm of the Democratic Party'

The truth is that the Democratic Party is an arm of the Unions.
 That is my take on it.  Go read the article.  Poor union is mad at the Democrats, the Democrats are mad at the union for spending money on someone other than their candidate. This is the dispute:

The major labor federation AFL-CIO took sharp objection tonight to a White House official's assessment that they'd "flushed $10 million of their members' money down the toilet" in the "pointless exercise" of supporting the failed bid of Bill Halter to unseat Sen. Blanche Lincoln.

They really have some nerve in talking about how much money was spent,they are telling us how corrupt they are. This was provided by union dues. In many cases union dues paid in because they must pay the dues or be penalized.  When will teachers and others realize if they could keep that money they could spend it on something besides union bigwigs and politics. Money they could spend on their own children, their own homes, their own lives.