A coalition of retired military generals has sent a letter to the U.S. Senate calling on them to reject an attempt by the House of Representatives to limit the military’s ability to use alternative fuels if they cost more than fossil fuels.

The provision, called the Conway amendment to the Defense Department budget, was passed by the House on May 15. It also attempts to dismantle the 2007 alternative fuels requirements for government energy consumption.

In a letter to Carl Levin, chairman of the Senate Armed Services Committee, the generals warned that the country’s reliance on oil is a serious threat to national security and called on Congressional leaders to support the military’s lead in developing the next generation of secure, clean energy sources. Every day, the United States sends $1 billion overseas for oil, which the generals say is draining the economy and strengthening the country’s enemies.

“We cannot drill our way out of the problem of energy security,” they said in the letter. “Even if we flood the market with every drop of oil in both our proven and strategic reserves, it will not be enough to offset rising global demand. Gas prices would still remain high and OPEC would continue to set the international price of oil.”

The retired generals who signed the letter to the Senate are part of a coalition of veterans, dubbed Operation Free, that recognize climate change and energy dependency pose serious threats to U.S. national security and support acting quickly to develop new clean sources of domestic energy production, including the use of advanced biofuels in military transport. “The Navy is investing in advanced biofuels programs that will enhance its power-projection capability,” the letter states.

The military, and especially the Navy, has been at the forefront of supporting the development of advanced biofuels. The Navy wants to get 50 percent of its energy from low-carbon emitting alternative fuel sources by 2020, and has invested heavily to help develop bio-based diesel and aviation fuels. The military is also concerned with its ability to supply to supply the energy needs of its troops on the ground, which can cost upwards of $400 per gallon and carries mortal risks for its transport.

Separately, the Obama administration has also threatened to veto the bill if the provision to limit the military’s use of alternative fuels was left in the bill. In a statement, the Office of Management and Budget said, “if the cumulative effects of the bill impede the ability of the Administration to execute the new defense strategy and to properly direct scarce resources, the President's senior advisors would recommend to the President that he veto the bill.” The OMB review concurred with the retired generals finding that the House bill as it stands, would affect the military’s ability to procure alternative fuels, increase the country’s reliance on fossil fuels, “thereby contributing to geopolitical instability and endangering our interest abroad.”