Follow Live: Voting Rights Bill Debate Updates

The move, which comes after other groups said they would no longer endorse Democrats who do not support ending the filibuster, is intended to pressure the Senate holdouts who have opposed the change — Senators Kyrsten Sinema of Arizona and Joe Manchin of West Virginia. It also represents a moment of open intraparty warfare.

Mr. Manchin and Ms. Sinema oppose changes to the filibuster, arguing the move would upend decades of tradition protecting minority party’s rights and lead to greater dysfunction in the Senate. Ms. Sinema has said she believes Democrats would regret the move the next time Republicans control the chamber.

A statement from Stand Up America, one of the many grass roots groups that helped Democrats in the 2018 midterm elections, invoked Dr. Martin Luther King Jr.’s writing on the “dangers of the white moderate.”

“While Black and brown voters face increasing attacks on their freedom to vote, Senators Manchin and Sinema continue to accept delay and inaction as they maintain their defense of the Jim Crow filibuster and wait for Republican support of voting rights that is not coming,” the statement said.

Emily’s List, the largest funder of female Democratic candidates who support abortion rights, threatened to pull its funding of Ms. Sinema if she refuses to change the filibuster. NARAL Pro-Choice America, another prominent abortion rights group, quickly followed, saying it wouldn’t endorse senators who don’t “support changing the Senate rules to pass voting rights legislation.”

Jamal Raad, executive director of the Evergreen Action Fund, a climate group that released a statement urging Congress to act on voting rights, said: “The Senate must pass both bills — and change any antiquated Senate rule standing in their way.”

“It’s not one crisis over another, these issues are interwoven — Congressional leaders must show that they can walk and chew gum at the same time,” Mr. Raad said.

Earlier this week, other well-known political activists were arrested at the U.S. Capitol Building as they held a sit-in urging Ms. Sinema and Mr. Manchin to change their stance. They said they were carrying out the mission of past civil rights leaders.

“We are coming together to honor the tradition of John Lewis and engage in good trouble to redeem the soul of this nation and protect our democracy,” said The Rev. Stephen Green, who chairs a group called Faith for Black Lives and was arrested in Washington.

“Now is the time for the Senate to go on record and vote to determine whether or not this country will choose fascism or choose democracy,” he said.

The crescendo of criticism is likely to intensify as Democrats plow ahead with a vote this week on two voting rights proposals, which would give the federal government more power to combat state election laws that make it harder to vote, change redistricting laws, and give states more tools to expand access to mail-in balloting and early voting.

However, under current Senate rules, the bills would either need Republican support or a change to the filibuster, allowing Democrats to pass the measures with just 51 votes. Mr. Manchin and Ms. Sinema have long said they oppose changing Senate rules. Ms. Sinema restated her opposition last week in a floor speech. Mr. Manchin has done it repeatedly for months.

This week, when asked about the activist criticism and pressure, Mr. Manchin was unfazed.

“It’s rough and tumble,” he said to reporters at the Capitol. “We’re used to that. Bring it on.”