Council Speaker Melissa Mark-Viverito and labor leader Delores Huerta tore into Vermont Sen. Bernie Sanders over his past votes on immigration issues—and to defend Hillary Clinton’s record on the issue.

Appearing outside City Hall, the two Latinas savaged Mr. Sanders as historically unsympathetic and even hostile to Latinos, and a poor choice for Hispanic voters in the April 19 New York primary. Ms. Mark-Viverito, a native of Puerto Rico, and Ms. Huerta—a Mexican-American who co-founded the United Farm Workers with Cesar Chavez—are both ardent backers of Ms. Clinton, the Democratic front-runner.

“It’s important that New Yorkers understand that, while Hillary Clinton has been fighting for us her entire life, Senator Sanders has not only been entirely absent from our community, but has also stood on the wrong side of the issues that matter most to Latinos,” she said. “The reality is that Latinos and immigrants have never been a part of Sanders’ vision for America.”

In particular, the speaker assailed the self-described democratic socialist for opposing the Comprehensive Immigration Reform Act of 2007, which had the support of Ms. Clinton, Massachusetts Sen. Ted Kennedy and then-President George W. Bush. She also attacked Mr. Sanders for backing the 2006 Community Protection Act—which, according to the Congressional Research Service, would have permitted “indefinite detention of specified dangerous aliens”—and for voting in favor a 2006 amendment in the House that banned the U.S. government from notifying Mexican authorities about the activities of the border-patrolling Minutemen group.

“When given the option, Sanders turned his back on Latinos. When given the option, Sanders sided with the anti-immigrant right. And when given the option, Sanders voted against—voted against—keeping Latino and immigrant families together,” Ms. Mark-Viverito continued. “We need a leader who has always stood by Latinos, and who has always valued our contributions to this country.”

Most unions and the League of United Latin American Citizens opposed the 2007 proposal because of its expanded guest worker program, which the organizations complained would lead to “exploitation.” Most of the House Democratic conference voted in favor of the Community Protection Act.

Mr. Sanders has defended his vote on the Minutemen amendment by arguing it simply confirmed existing law. But it placed him in the company of a number of conservative members of the House of Representatives, where Mr. Sanders represented Vermont prior to his 2008 election to the Senate.

The underdog candidate’s team did not immediately respond to requests for comment.

Ms. Clinton’s record on immigration issues is also mixed. As senator from New York, she voted in favor of the Secure Fence Act of 2006, which created a new 700-mile barricade along the Mexican border. Mr. Sanders voted against that legislation.

When running for president in 2008, Ms. Clinton voiced opposition to a proposal by then New York Gov. Eliot Spitzer to provide drivers licenses to undocumented immigrants. Ms. Mark-Viverito defended the candidate’s past stance, noting that she has since changed her position.

The speaker argued that the drivers license debate was “a different conversation” than the “unique window” the 2007 immigration reform bill offered. Ms. Huerta agreed that the 2007 bill was an irretrievable chance to grant legal status to the 11 million undocumented immigrants in the U.S.

“That was our big opportunity. And then Senator Sanders came out against us. And because he was supposed to be one of the most liberal people in the Congress, that really hurt our chances of passing that bill,” Ms. Huerta said, dismissing the socialist candidate’s often lofty rhetoric. “Talk is cheap, right? Talk is cheap.”

Ms. Huerta’s attacks are particularly interesting given the UFW’s harsh rhetoric and stances toward the undocumented during its period of peak activity in the late 1960s and early 1970s. Curiously, the labor leader denied that history entirely when asked about it today.

“That’s just not true,” she said, noting that the union helped undocumented members get legal status in the early 1960s, and has lobbied for immigration reform since the 1980s.

Despite Ms. Huerta’s disavowal, it is a well-documented fact that in 1973, several hundred UFW members established what they described as a “wet-line” along the Mexican border in Arizona to prevent immigrants from crossing over—not unlike the Minutemen’s patrols four decades later. In 1974, the union inaugurated its “Illegals Campaign,” in which it urged members to report undocumented workers to federal authorities for deportation.

In the 1986, badly reduced in size and influence, the UFW endorsed President Ronald Reagan’s plan to grant amnesty to some four million foreign nationals residing in the country without proper paperwork.

Earlier today, Ms. Clinton announced her intention to create a federal Office of Immigrant Affairs. When the Observer asked if she accept a hypothetical opportunity to helm that new department, Ms. Mark-Viverito declined to answer.

“Is there another question?” she asked.