A key member of a new bipartisan panel charged with cutting the deficit said he’d walk away from the group’s work if the process results in deeper cuts to the military.

Speaking to a conference organized by the American Enterprise Institute and the Heritage Foundation in Washington, Sen. Jon Kyl (R-Ariz.) said he would quit the so-called supercommittee if the group moves to cut more deeply into defense spending, according to several reports.

The comments came on the same day the group sounded an optimistic tone at its first meeting, with members promising to keep an open mind about how to meet their legal mandate to cut $1.2 to $1.5 trillion from the deficit over the next decade.

But Kyl told the gathering of conservative think tanks that he was “off the committee” if it seeks to cut defense more deeply, Politico reports.

“My point of view is that defense should not have any more cuts,” he said.

Under the deal that created the supercommittee, Congress agreed to cut nearly $1 trillion from discretionary spending over the next decade. By imposing spending caps separately on security and non-security areas of the budget, they ensured the military would take a significant portion of those cuts.

If the supercommittee cannot agree on a strategy to reduce the deficit by at least $1.2 trillion more over the next 10 years, the budget would be automatically cut by that amount. Half would come from the military, a prospect that has the Pentagon and congressional hawks deeply nervous.

Kyl’s warning contrasted with the far cheerier tone set at an opening meeting for the committee Thursday, where members promised that they would not draw any lines in the sand to start the process.

But of the 12 senators and representatives, there too Kyl was the most cautious. A veteran of several rounds of previous deficit reduction talks, Kyl told his colleagues that it was necessary to bring a “dose of realism” to the effort.

“This is tedious, time-consuming work,” he said. “It’s going to require going through a lot of budget numbers line by line.”

But with his colleagues, he said he was struck by how united the group seemed to be and said he hoped that they could tackle entitlement and tax reform, coming up with a package of savings that would eclipse the committee’s $1.5 trillion goal.