Forty-six members of Congress, including Colorado Democratic Reps. Jared Polis and Diana DeGette, sent a letter to former Colorado senator and current Interior Secretary Ken Salazar Thursday backing the disclosure of secret chemicals used in the controversial natural gas drilling process called hydraulic fracturing, or “fracking.”

Polis and DeGette, along with Rep. Maurice Hinchey, D-N.Y., co-sponsored the Fracturing Responsibility and Awareness of Chemicals (FRAC) Act in 2009, only to see it languish in the overall gridlock over energy policy and climate-change legislation. Dubbed the “Haliburton Loophole” for the oil services company that perfected the process, fracking was granted an exemption from the Safe Drinking Water Act during the Bush-Cheney administration in 2005.

It involves injecting water, sand and undisclosed chemicals deep underground to fracture tight geological formations and free up more natural gas. Haliburton and other companies say they must keep chemical formulas secret for proprietary reasons and that the process is safe. Critics say fracking has led to contamination of drinking water.

The Interior Department is weighing a proposal to require chemical disclosure in all fracking operations conducted on public lands through the oil and gas leasing process.

Earthjustice Legislative Associate Jessica Ennis called that plan “a crucial step in pulling back this veil of secrecy. The support for the public’s right-to-know, championed by [Hinchey, DeGette and Polis] and echoed by their colleagues is invaluable — as is their tireless work to restore drinking water protections for communities all over the country that have been placed in harm’s way by rushed and irresponsible gas development.”

The fracking debate has grown increasingly heated on Colorado’s Western Slope, where property owners say well water is being impacted by the process.