Look for the UNION LABEL and then REFUSE to buy it...
The Union Label Directory provides the Local Unions of this International Association, and their signatory contractors, a way to identify the companies that manufacture products for the construction industry that bear our union label. There are two different colored labels.
The BLUE label is for products made under production contracts. The YELLOW label is for products made under building trades contracts.
The products listed in the directory are created entirely by members of the Sheet Metal Workers' International Association, and the companies listed are all eligible to use the union label on their products. This directory is revised and updated periodically. Click here to use the Union Label Directory.
http://www.smwia.org/union_label_directory/union_label_dir.asp
Unfortunately if you do that you also hurt a lot of rank and file Republican workers....that's right...my ex-husband (a teamster) and lots of his friends are Republicans who unfortunately have no say in what the national union does and says.