Corrected 5:15 p.m. | The Census Bureau said it will cut short its counting efforts by a full month, a move experts say risks a massive undercount of immigrants, minorities, rural residents and other hard-to-count groups.

The agency had planned to conduct its largest operation — 500,000 or more staff knocking on the doors of households that haven’t completed the census questionnaire — from now through October, and delay the delivery of results to March. However, the agency will now stop counting on Sept. 30 to meet its original Dec. 31 deadline, Census Bureau Director Steven Dillingham said in a Monday night statement.

“The Census Bureau’s new plan reflects our continued commitment to conduct a complete count, provide accurate apportionment data, and protect the health and safety of the public and our workforce,” Dillingham said.

Congressional Democrats and advocates blasted the administration’s move, saying it would shortchange the census for political advantage. Rep. Carolyn B. Maloney, D-N.Y., introduced legislation Tuesday to mandate the agency follow its planned extended timeline and asked eight agency officials to sit for interviews before the House Oversight and Reform Committee she chairs.

“I am concerned that the administration is seeking to rush the process and sacrifice the accuracy of the census for political gain, that the president’s intent is to have all of this done before he leaves office, so that he can do what I believe is an illegal action,” Maloney said last week during a hearing she chaired.

Advocates and former census officials said truncating the in-person counting period may make it more likely that populations deemed “hard-to-count” will be missed, skewing the numbers for a decade. Former Census Bureau Director John Thompson said during the same hearing July 29 that rushing the process could mean the agency relies more on administrative records and statistical imputation to arrive at a final count. Those methods are more likely to leave out immigrants, young children, rural residents, the homeless and other groups.

The director of New York City’s census effort, Julie Menin, called the schedule change “a disgusting power grab” by the administration. The city’s response rate currently stands at 54 percent.

“From day one, it has been abundantly clear that Donald Trump is going to try everything possible to stop New Yorkers from filling out the census, and now, amid a global pandemic that’s severely impacted outreach, they are straight-up trying to steal it,” Menin said in a statement Monday.

Los Angeles city attorney Michael Feuer, already suing the administration over the attempt to exclude undocumented immigrants from apportionment, questioned the potential delay before Monday’s announcement in a letter to the agency.

“I am deeply concerned that the Census will be tremendously inaccurate — with sweeping, deleterious consequences for the proper determination of vital public funding allocations and political representation,” he wrote.

Current law requires the Census Bureau to complete the count by Dec. 31, but the agency postponed most operations for months amid the coronavirus pandemic. To adapt to the delays, the agency altered its schedule and asked Congress to amend the law so that results could instead be delivered by the end of March.

[Trump signs memo to exclude undocumented immigrants from census]

The House previously passed the deadline extension last month as part of its latest coronavirus relief package, but the Senate has not acted on that measure. For months, senior Census Bureau officials have said they are past the point where they could comply with the current December deadline.

Last month, Trump signed a memorandum directing the Commerce Department to exclude undocumented immigrants from the totals used to divvy up congressional seats. The move already faces half a dozen lawsuits that argue it violates the Constitution.

A relief bill the Senate introduced on July 27 had $448 million for the Census Bureau’s continued operations, but no deadline extension.

Some Senate Republicans on Tuesday said they may want to looker closer at the agency’s decision. Sen. Shelley Moore Capito, R-W.Va., expressed concern about the potential for missing West Virginians in the count. And the chairman of the Senate Commerce-Justice-Science Appropriations Subcommittee, Sen. Jerry Moran, R-Kan., said he asked the Census Bureau to provide any documents justifying the new timeline.

“We want to be assured that everything is being done to get an accurate and full … census count, and would not want to do anything that might diminish that chance,” Moran said. “At the same time we want to be cautious because of COVID-19.”

More than 62 percent of households nationwide have responded to the census on their own as of census data released July 30. However, rural areas and cities have lagged behind on the count. Alaska currently has a 49 percent response rate, the lowest in the nation.

In addition to reapportionment data, census results are also used to draw legislative maps, guide $1.5 trillion in federal spending annually and undergirds private survey data.

Several former directors of the Census Bureau told members of Congress during last week’s hearing that any truncation of the counting process could jeopardize the usefulness of the census results. Kenneth Prewitt, who oversaw the 2000 census, said a rushed process risks making the census results entirely unusable.

“The chances of having a census accurate enough to use is unclear, very very much unclear whether we will even have a census,” Prewitt said. “That’s why the debate about illegals or undocumented is beside the point if we’re not even going to have a census that we can take to the American people. That’s what I’m worried about.”

Lindsey McPherson contributed to this report.

Correction: This report was revised to correct the date the Senate relief bill was introduced and the timing of a presidential memorandum regarding undocumented immigrants.