A senior House Democrat is threatening to subpoena Commerce Secretary Wilbur Ross over the Commerce Department’s failure to release documents related to the 2020 Census, saying anomalies in the survey are “more serious than first reported” and blasting the department for ignoring requests for information.

In a scathing letter to Ross on Wednesday, House Oversight and Reform Committee Chairwoman Carolyn B. Maloney (D-N.Y.) said three internal documents showed that “career officials have now identified at least 15 anomalies that impact more than one million Census records.”

The letter, which comes a day before a committee hearing is scheduled on the matter, excoriated Ross for repeatedly dodging requests for information about the census in recent weeks and over the course of his tenure.

“Your failure to cooperate with the Committee’s investigation appears to be part of a dangerous pattern of obstruction with the Census,” Maloney wrote, later adding, “You personally have played a key role in blocking the production of information to the Committee regarding the Trump Administration’s efforts to politicize the 2020 Census—even after it was subpoenaed.”

Maloney said Census Bureau Director Steven Dillingham, who reports to Ross, dodged a request she made last month for documents related to data-processing anomalies and scheduling. She set a new deadline of Dec. 9 for the documents. If that request is ignored, she will subpoena Ross and may consider holding a second hearing to hear directly from him, according to a senior Democratic committee aide.

Trump had hoped to receive the data in time to try to exclude undocumented immigrants from being counted for a decade’s worth of apportionment of House seats before he leaves office Jan. 20.

But internal documents obtained by the committee indicate that the bureau needs until at least Jan. 23, 2021, to transmit apportionment figures to the president, Maloney wrote. That is more than three weeks after the statutory deadline for delivering the data.

The Census Bureau, in a statement issued Wednesday evening, said, “Internal tracking documents would not convey the uncertainty around projected dates and may fail to reflect the additional resources employed to correct data anomalies.”

The agency added: “The anomalies affect less than seven-tenths of one percent of records and are being resolved as expeditiously as possible.”

To try to carry out his plan, the president would need to receive two sets of numbers — the total population counts and the number of undocumented immigrants in each state. But the internal documents cited in Maloney’s letter said the bureau would need until at least early February to transmit a tally of undocumented immigrants by state.

Lawyers for the administration have not been able to answer questions from judges about how the government plans to count undocumented immigrants in each state, or whether it is even possible to do so. A comprehensive list of undocumented immigrants does not exist, and by law apportionment numbers must be based on an actual enumeration, not estimates.

In addition to apportionment, decennial census data is used to determine a decade’s worth of federal funding and state redistricting.

The Supreme Court heard arguments Monday about Trump’s apportionment plan after three federal courts blocked it, saying it was unlawful, and in one instance unconstitutional. A fourth federal court said it was too early to judge the merits of the case.

Maloney last month asked Dillingham to produce documents by Nov. 24 related to when the bureau could deliver state population totals. Her request followed leaked reports that the data would not be ready until late January or possibly into February.

Maloney wrote Wednesday that a Nov. 19 internal Census Bureau document described 13 anomalies that affect more than 900,000 census records, including some that could result in undercounts and other inaccuracies.

The document said that addressing the anomalies “impacts overall end date by 20 days” and anticipates that the population count will not be complete until between Jan. 26 and Feb. 6, adding that if new anomalies were identified, more time may be required. It outlined an 11-step process for correcting the anomalies and “cautions that taking shortcuts could compound these problems and lead to even more errors.”

A second internal document a week later said additional errors had been discovered, including one affecting over 240,000 records, the letter said.

The once-a-decade survey was delayed by the coronavirus pandemic, and the government had initially requested an additional four months to produce it. But after Trump issued a memorandum in July saying he would try to exclude undocumented immigrants, the bureau had scrambled to finish the count and process the data by Dec. 31, sparking lawsuits and resulting in what many enumerators said was a rushed and often sloppy effort to reach the hardest-to-count households.

After initially proposing to expand the five-month post-count processing period, the government condensed it to about half that amount of time, causing alarm among statistics experts who warned it could result in an inaccurate count.