In a Nov. 30 letter, union head J. David Cox said that the Cato Institute used “bad math” in finding that government workers are overpaid. But the Federal Salary Council (FSC) study he cited suggesting that federal workers are 35% underpaid is way out of line with statistical studies by the Congressional Budget Office (CBO) and many other experts.

Compared with private-sector workers, CBO found that federal workers are overpaid on wages by 2%, on average, and overpaid on benefits by a whopping 48%. Federal workers have gold-plated retirement plans, high job security and other advantages.

Why are the results of the union-favored FSC study so different than other studies? Congress should hire an expert accounting firm to independently audit FSC’s opaque methodology and find out.

This letter originally appeared in the Wall Street Journal