Two Democratic senators Tuesday further endangered the chances of a bipartisan infrastructure deal by promising to vote against any legislation that doesn't include a "bold" effort to address climate change. 

Sens. Jeff Merkley, D-Ore., and Ed Markey, D-Mass., made the comments at a Tuesday press conference, joining Sen. Bernie Sanders, I-Vt., in opposition to a bipartisan infrastructure deal negotiated by moderates in each party. Because it takes 60 votes to clear a Senate filibuster, that means at least 13 Republicans will have to vote for the proposal if no more Democrats defect. 

"It's time for us to put on that classic song by Fleetwood Mac," Markey said of negotiations with Republicans, "time for us to go our own way." 

"We cannot let Republican calls for bipartisanship deny the American people the climate action they have been demanding," Markey added. "The GOP, who are the gas and oil party, would love nothing better than for these voters to be disillusioned by gridlock and inaction."

BIPARTISAN GROUP REACHES AGREEMENT ON INFRASTRUCTURE SPENDING FRAMEWORK

A Republican negotiating group led by Sen. Shelley Moore Capito, R-W.Va., was in talks with the White House for weeks on a potential infrastructure compromise before negotiations collapsed. But shortly after, a bipartisan group of senators put forward their own infrastructure proposal that reinvigorated hopes that a bipartisan deal could be passed by the current Congress. 

The agreement is largely focused on physical infrastructure projects and includes $579 billion in new spending, a source familiar with the deal's terms told Fox News. The plan would cost $974 billion over a five-year span and $1.2 trillion over eight years.

There were five Republican senators in that bipartisan group, meaning that unless five more Republicans got on board the agreement would not be able to pass under regular order in the Senate. But with at least three Democrats now defecting, the bar was just raised even higher. 

Markey warned that if Democrats continue down their current path, "we will fall into the Republican trap of delay and denial that will.... harm" any major action on climate change. 

"Energy investments cannot be left on the docks," Merkley added. "If there is no climate there is no deal." 

Republicans, meanwhile, say an infrastructure bill should be targeted at things like water, roads, bridges and broadband and they refuse to raise taxes to pay for it. 

"Look, both sides would like to get an infrastructure bill. Here are the red lines on our side. We’re not going to reopen the 2017 tax bill," Senate Minority Leader Mitch McConnell, R-Ky., said on the Hugh Hewitt radio show Monday. 

Sen. Ed Markey, D-Mass., holds a news conference outside the Supreme Court to announce legislation to expand the number of seats on the high court, on Capitol Hill in Washington, Thursday, April 15, 2021. Markey on Tuesday said he will oppose any infrastructure bill that doesn't address climate change. (AP Photo/J. Scott Applewhite)

Sen. Ed Markey, D-Mass., holds a news conference outside the Supreme Court to announce legislation to expand the number of seats on the high court, on Capitol Hill in Washington, Thursday, April 15, 2021. Markey on Tuesday said he will oppose any infrastructure bill that doesn't address climate change. (AP Photo/J. Scott Applewhite)

On paying for the legislation, he added, "States and localities are literally awash in extra money. A lot of that is still in the pipeline. Why don’t we repurpose that, earmark it for infrastructure, which both localities would prefer to spend it on anyway? And that would be a good way to get a pretty robust infrastructure bill on a bipartisan basis without raising taxes."

Markey was careful Tuesday to avoid explicitly rebuking Senate Majority Leader Chuck Schumer, D-N.Y., or President Biden, who he said "want a very strong climate infrastructure bill to pass." But, Merkley said, any dual-track plan for one hard infrastructure bill Republicans can vote for and a separate climate-related bill must be "welded together" to guarantee the Senate passes a climate bill. 

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"There absolutely has to be a guaranteed deal that climate is built into," Markey said. "We can't have dessert before the main course. The main course is a climate infrastructure bill. We need roads, we need bridges, we need many other things… But we can't leave the climate behind." 

The demands from Merkley and Markey may also reflect the political reality in the House of Representatives, where some members warned Tuesday it may be tough to get all House Democrats on board with a compromise that comes out of the Senate. 

"If there was to be, by some miracle, a smaller bipartisan deal, I think it would be very difficult to find the votes for that in the House," barring a "full reconciliation package," House Progressive Caucus Chair Pramila Jayapal, D-Wash., said. 

Fox News' Thomas Barrabi, Jason Donner and Jacqui Heinrich contributed to this report.