On Friday dozens of progressive nonprofits wrote a letter to Senate Majority Leader Chuck Schumer demanding he take steps to eliminate the Senate filibuster.

The nonprofit activist groups are considered "dark money" groups as the sources of their funding are unknown.

"Voters across the country have made their voices loud and clear, culminating in the strong message that was recently delivered in Georgia," the coalition of liberal groups wrote. "They are sick and tired of the gridlock and dysfunction that is keeping the system rigged against them."

"To be clear, the filibuster was never intended to be used and abused the way it has been over the past decade. Despite what some will claim, the filibuster isn’t in the Constitution," the letter continued.

The Senate filibuster requires 60 votes to end debate on most legislation, and supporters argue it’s necessary to maintain the upper chamber as the most deliberative body in federal government.

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With the Senate split 50-50 and Vice President Kamala Harris offering a tie-breaking vote, Sen. Minority Leader Mitch McConnell fought hard to get Schumer to rule out ending the super-majority hurdle. He dropped his request when Sens. Joe Manchin, D-W. Va., and Kyrsten Sinema, D-Ariz., came out in opposition of eliminating it.

"Until recently, the filibuster was only very rarely used to block ordinary legislation supported by the majority of senators," the letter read. "The exception, of course, was its deplorable use as a tool to block civil rights, voting rights and anti-lynching bills, which is why President Obama correctly referred to it as a 'Jim Crow relic.'"

The letter pointed to the Republican majority in 2017 eliminating the filibuster to confirm President Trump’s Supreme Court nominees.

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Some historians say that the filibuster has been used to obstruct civil rights legislation in the past, but recently the more daring members of both parties have called to eliminate it, depending on who has the majority. McConnell had to resist calls from Trump during a Republican-controlled Senate to eliminate it.

Last week, a group of dark money groups announced a new "unrig the courts" coalition that will work to turn up the heat on Democrats to increase the size of the Supreme Court, enact term limits for the high court and expand lower federal courts.

"Donald Trump and Mitch McConnell were terrifyingly successful in transforming the judiciary into an arm of the Republican party," said Meagan Hatcher-Mays, director of democracy policy at Indivisible. Under the Trump administration, 187 new judges were confirmed.

President Biden benefited from a record-shattering amount of "dark money" donations during the 2020 election.

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A report published by Bloomberg News shows that Biden raked in about $145 million in donations from anonymous donors to outside groups backing him, far outstripping the $28.4 million spent on behalf of his rival, former President Donald Trump. It also tops the previous record of $113 million in dark money donations spent on behalf of Republican presidential nominee Mitt Romney in 2012.