The White House on Thursday threatened to veto a Republican-backed spending bill that would defund Obamacare, intensifying fears of a government shutdown.

“It advances a narrow ideological agenda that threatens our economy and the interests of the middle class,” the Office of Management and Budget said in a statement about the House continuing resolution. “The resolution would defund the Affordable Care Act, denying millions of hard-working middle class families the security of affordable health coverage.”

It is unlikely the White House will actually have to use its veto as the GOP measure stands little chance of passing the Democratic-controlled Senate.

The veto threat, though, represents the latest round of sparring between the White House and congressional Republicans ahead of a October deadline to keep the government funded and ahead of the U.S. hitting its borrowing limit later that month.

Obama defended his signature legislative achievement in remarks to his Export Council Thursday, saying the law was “starting to bear real fruit.”

Speaker John Boehner, R-Ohio, countered that the law is a “train wreck” the American people wanted to eliminate.