On Wednesday, the New York Immigration Coalition, an activist group, announced its New York Counts 2020 campaign alongside congressional and local elected officials. The effort has three prongs: to fight the question; to pressure the United States Census Bureau to protect the information of all New Yorkers; and to reassure residents that they can safely respond.

At the news conference, Nydia Velázquez, a Democrat representing Queens, Brooklyn and Lower Manhattan, said she is co-sponsoring legislation in the House of Representatives that will require the Commerce Department to provide advance notice to Congress before changing questions on the census. Representative Grace Meng, a Democrat from Queens who sits on the committee that funds the census bureau, said she and her colleagues are considering withholding funds for 2019 unless the question is removed.

In a public hearing last week before the question was added, Ms. Meng confronted the Secretary of Commerce, Wilbur Ross, whose department oversees the U.S. Census Bureau. “I told him directly that this is about accuracy; this is mandated by the Constitution to count every living person.”

New York Mayor Bill de Blasio said that he would join the multistate lawsuit brought by the state’s attorney general, Eric T. Schneiderman, against the Trump administration, to try to block the question from being included.

In the last census count, in 2010, the city’s response rate was 62 percent, but some heavily immigrant communities, like Washington Heights and the South Bronx, exceeded that, with more than 70 percent of residents answering the census questionnaires.

Adriano Espaillat, a Democrat who in 2010 was representing Washington Heights and Harlem in the State Assembly, said that was in part because of a robust effort by volunteers to convince residents their participation counted. Mr. Espaillat, who is now in Congress, said he could not yet encourage undocumented residents to take part.

“I want to fight this question back, first,” he said. “If not in Congress, then in the courts. If at the end of this the question remains, then we’re going to have to come together to decide the messaging.”