The top U.S. derivatives regulator is used to battling Wall Street. Now it's gearing up for a potential fight with its own employees.

In February, the Commodity Futures Trading Commission (CFTC) contracted to spend as much as US$420,000 on outside labor lawyers after its workers joined a union, public documents show. The CFTC retained the attorneys in case labor negotiations break down and the agency becomes embroiled in a legal dispute, said a person briefed on management's thinking who requested anonymity.

Tensions within the CFTC reached a flashpoint in December when employees grilled Chairman Timothy Massad about their compensation and benefits at an agency-wide meeting. The unrest comes at a pivotal time for the CFTC, which was transformed by the 2010 Dodd-Frank Act from a regulator of mainly agriculture futures to a front-line cop of the $700 trillion swaps market.