Rep. Chris Van Hollen (D-Md.) received the endorsement of the largest immigrant advocacy group in the region on Tuesday. (Marvin Joseph/The Washington Post)

The political arm of the immigrant advocacy organization CASA of Maryland announced Tuesday that it is backing U.S. Rep. Chris Van Hollen (D-Md.) in the U.S. Senate race to succeed retiring Sen. Barbara A. Mikulski (D).

The endorsement comes one day after Emily’s List, a national abortion rights women’s group, said it would spend $1 million in media ads for Rep. Donna F. Edwards (D-Md.), Van Hollen’s primary rival.

“Having worked closely with Chris since 2001, I know he is ready to challenge the status quo to advance justice,” Gustavo Torres, president of CASA in Action, said in a statement.

The pro-immigrant group, the region’s largest, said that although it recognizes the strengths of both candidates, Van Hollen’s “deep engagement in several high profile immigration relief cases” and record advancing immigrant rights weighed into backing the longtime Maryland lawmaker.

Edwards has struggled to raise money at the same pace as Van Hollen, and a poll in November by the Baltimore Sun showed her trailing her opponent by 14 points. A Washington Post-University of Maryland poll in October, however, showed Edwards in the lead.

Support from CASA and its thousands of volunteers could provide a boost to candidates seeking to tap into Maryland’s eligible Hispanic voters, who number more than 165,000.

Its political field-organizing operation mobilized Latinos in large numbers in elections in 2012 and 2014, lifted by pro-immigrant ballot initiatives, such as the state Dream Act, which grants an in-state tuition discount to undocumented college students.

“I’ve been proud to work with CASA on so many important issues facing our community — from comprehensive immigration reform to health care to community safety and workforce training,” Van Hollen said in a statement. “We’ve made important progress, but there is more to be done to achieve economic opportunity and justice for all.”

Both Van Hollen and Edwards represent congressional districts with some of the largest concentration of Latinos in the state, and both supported the Dream Act.

They also joined House Democrats in filing an amicus brief defending President Obama’s executive actions to shield millions of illegal immigrants from deportation. Last month, a federal appeals court ruled against the program, Deferred Action for Parents of Americans, allowing eligible immigrants to remain here and work.

But immigration isn’t the only issue Latino voters care about. Research shows that like many voters — of any ethnicity or race — education, health care and employment are at the top of the list of concerns for Latino families.