A letter from 80 Republicans asked Speaker John Boehner, R-Ohio, to resist any spending bills that would accommodate the new health care law, which is nearing a critical stage of signing up millions of Americans for health coverage.

Because it’s virtually certain that President Barack Obama and the Democratic-controlled Senate would reject such demands, leaders of both parties say the standoff likely would result in a partial shutdown of the federal government, similar to those that occurred in 1995 and 1996.

The letter is mixed news for Boehner and other GOP leaders who view a government shutdown as politically unwise.

With 80 of the House’s 233 Republicans signing the letter, a solid majority of 153 has refrained from trying to limit Boehner’s options. That presumably would allow the speaker to push a bipartisan bill that funds the health law and is supported by a “majority of the majority” of his fellow Republicans, which Boehner says is essential.

However, he would need more than 60 Democratic votes to pass such a bill. That would give Democrats a major voice in its details.

The federal 2013 fiscal year ends Sept. 30. New money must be appropriated by then to avoid a shutdown of countless government offices and agencies.

Voters chiefly blamed congressional Republicans for the mid-1990s shutdowns, and the fallout boosted Democratic President Bill Clinton. Ever since, many establishment Republicans have urged the party to avoid using shutdown threats as a bargaining tool.

But a new generation of tea party-backed conservatives rejects the advice. They say “Obamacare” — officially the Affordable Care Act — is so unpopular and unworkable that it justifies extraordinary tactics to block it.

A possible solution to the budget impasse, often used in past years, would involve a “continuing resolution” to keep funding the government at current levels. Many top Republicans, including Senate Minority Leader Mitch McConnell, say it’s impossible to carve out money for “Obamacare” in any appropriations measure.

The House letter was authored by Rep. Mark Meadows, R-N.C. It urges Boehner “to affirmatively de-fund the implementation and enforcement of Obamacare in any relevant appropriations bill,” including “any continuing appropriations bill.”

At least a dozen Senate Republicans have signed a similar letter.

In recent years, Democrats and Republicans in Congress repeatedly have failed to reach major compromises on spending. A string of secret negotiations with the White House, a bipartisan “super committee” and various threats of economic calamity have all proved fruitless.

The impasses led this year to automatic, across-the-board spending cuts known as sequestration, which have hampered some federal agencies and helped shrink the deficit.

Some House Republicans want deeper cuts still. But others revolted this summer when popular programs were targeted.

Senate Democrats want to replace the sequester cuts with a more generous spending plan, but House Republicans vow to block it.