WASHINGTON — The Census Bureau will cease door-knocking and other field activities for the 2020 Census a month earlier than planned, raising concerns among civil rights organizations that the constitutionally required population count will be inaccurate, particularly in its count of minorities and immigrants.

The move represents an about-face by the Trump administration, which had originally supported extending the data collection and processing until next year because of the coronavirus pandemic. Critics said the decision, announced late Monday as field activities are underway, was in keeping with broader attempts by the administration to alter the census for partisan gain.

“The administration has now done a complete 180 without any warning,” Sarah Brannon, managing attorney for the American Civil Liberties Union’s Voting Rights Project, said Tuesday. “I think this decision is consistent with the behavior all along in politicizing the census and marginalizing the importance of the census.”

Rep. Jimmy Gomez, D-Calif., who introduced legislation earlier this year with the Trump administration’s backing to push back the deadline, said the administration’s efforts to manipulate the results were unprecedented. He also said the maneuver could backfire.

Gomez said that if the counting were to be stopped now, for example, it probably would result in his state picking up additional congressional seats. Gomez, who studied census history in graduate school, said it’s also possible that by rushing the data collection, the census could also undercount rural areas where the president has a steadfast base of support.

“People think that they can manipulate the census, but you never truly know how it’s going to turn out if you try to do it,” Gomez said.

As of Monday, about 93 million households, or nearly 63 percent of the country, have responded to the census.

In March, many field activities were shut down because of the pandemic. The Trump administration in April requested four additional months to complete data collection. Field activities, including online and telephone reporting, resumed in June, and the nonresponse follow-up phase was expected to begin in mid-August and run through October. It will now end Sept. 30, and the bureau will submit the population count to the president by Dec. 31.

Plans to shut down the count earlier drew fierce criticism from Democrats and civil rights groups, which have pushed back against a broader effort by the Trump administration to change how the population is counted and how the data is used. In 2018, the administration had pushed to include a citizenship question on the census, a move blocked by the Supreme Court last year.

“This is another deliberate attempt to undercount communities of color, immigrants, Native Americans, and other hard-to-reach groups,” Sen. Brian Schatz, D-Hawaii, said in a statement. He urged Congress to extend the deadlines.

“It is clear that the Trump Administration doesn’t want an accurate and full count. They want to deprive these communities of both political power and federal dollars for partisan gain.”

President Trump issued a July 21 memorandum saying undocumented immigrants should be barred from being counted for congressional apportionment. Legal experts say that would be unconstitutional.

Census Bureau Director Steven Dillingham issued a statement about 9 p.m. Monday announcing the earlier cessation of field activities, including the self-response option. He also said that monetary incentives would be offered to census takers to encourage them to work at maximum efficiency, and that additional staff would be hired and trained to accelerate data collection and processing apportionment counts ahead of the Dec. 31 deadline.

“Of course, we recognize that events can still occur that no one can control, such as additional complications from severe weather or other natural disasters,” Dillingham said. The bureau, according to figures released Tuesday, had nearly 84,000 temporary workers assisting with the count during the week of July 19.

But there have been reports that some enumerators, fearful of contracting the coronavirus, have quit.

Ellen Hoch, 61, of Berwin Heights, Md., said concern about the pandemic led to her decision to quit her job as an enumerator this week.

She said she signed up late last year before the pandemic and underwent training. But she has encountered a cumbersome and sometimes confusing process as census takers try to get a population count while protecting themselves from infection.

Instead of arranging appointments to meet with the management of assisted-living residences or group homes, she found herself having to go out on cold calls to obtain the data or dropping off mail-in surveys.

“One of the questions [during training] was, ‘Are you OK going into neighborhoods you’re not familiar with?’ Back then, I said I don’t mind knocking on people’s doors,” Hock said Tuesday. “But then the pandemic hit, and everything changed.”

Gomez said he held out hope that the Democratic-controlled House and the Republican-led Senate could still reach a compromise that extended the census deadline until April 2021.

“It’s really disappointing,” Gomez said. “But we’re not going to sit back and take it. … I hope the Republican leadership in the Senate are not so shortsighted as this administration.”

Rep. Carolyn Maloney, D-N.Y., who chairs the House Committee on Oversight and Reform, introduced additional legislative measures to hold the administration to the previous timeline for field activities.