What does it do? It identifies substances that are known or reasonably anticipated to cause cancer. They document their findings in their Report On Carcinogens (the ROC and yes, it includes ionizing radiation).
But what about the companies which earn their profits off the sales of a substance which has been added to the ROC? As in styrene or formaldehyde.
Well, first they take the standard science denial route, just like the tobacco industry did.
Next, find a politician who will bar funding of the ROC, someone who's shown a passion for ignorance.
Well, that was easy, Montana Rep. Rehberg (R).
They're also challenging the legal status of the ROC (see previous link). Ironically, the NTP was established in the 1970's based on Congressional concerns for the human health effects of chemicals in the environment.