(CNN) Leading progressives are threatening to reject a rules package backed by Democratic leadership over a requirement they believe could thwart their most ambitious policy plans.

New York Rep.-elect Alexandria Ocasio-Cortez and California Rep. Ro Khanna said Wednesday they will vote against any guidelines that include a provision known as "PAYGO," or "pay as you go," which requires that new spending be offset by matching cuts or increases in revenue.

Progressives who support programs like "Medicare-for-all" and other policies likely to increase government expenditures worry that the rule would create a self-imposed obstacle with limited political upside -- and come across as a sign that Democrats are committed to the austerity economics championed, at least rhetorically, by conservative groups.

Opponents of the rule say they would need 18 votes from the Democratic conference to scuttle the rules package, which is otherwise widely popular, and potentially send leadership into negotiations with the progressive holdouts.

"I do not understand why the Democrats don't have the courage of our convictions and make the case that our policies will lead to growth," Khanna said, arguing that the rule was ultimately a self-defeating political calculation: "PAYGO is to protect members in vulnerable districts who can say that Democrats are for fiscal responsibility. I'm all for raising taxes on the 1% and multinational corporations and stopping our excessive spending on the bad wars. But we should make an economic growth argument in swing districts instead of thinking the '90s playbook of fiscal responsibility will work."

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