Originally Published: 16 AUG 22 12:26 ET

Updated: 16 AUG 22 13:45 ET

By Annie Grayer, CNN

(CNN) -- Two top House Democrats are accusing the Department of Homeland Security Inspector General of obstructing their investigation into missing Secret Service text messages related to the January 6 Capitol attack, escalating tensions between Congress and the watchdog agency.

In a letter on Tuesday, House Oversight Chairwoman Carolyn Maloney and House Homeland Security Chairman Bennie Thompson, who also chairs the House January 6 committee, wrote to DHS Inspector General Joseph Cuffari, detailing claims of how Cuffari has not cooperated with their previous requests to provide documents or make his employees available for transcribed interviews in their ongoing investigation.

Maloney and Thompson have previously called for Cuffari to recuse himself from the investigation, saying they had lost confidence in him after he waited months to inform Congress that Secret Service text messages from January 6 had been erased.

"Your obstruction of the Committees' investigations is unacceptable, and your justifications for this noncompliance appear to reflect a fundamental misunderstanding of Congress's authority and your duties as an Inspector General. If you continue to refuse to comply with our requests, we will have no choice but to consider alternate measures to ensure your compliance," Maloney and Thompson wrote.

As CNN has reported, the Secret Service texts were erased as a result of a previously scheduled data migration of its agents' cell phones that began on January 27, 2021, exactly three weeks after the attack on the US Capitol.

In their Tuesday letter, Maloney and Thompson reveal that Cuffari wrote to them on August 8 informing them he would not be complying with their requests. "To protect the integrity of our work and preserve our independence, we do not share information about ongoing matters, like the information you requested in your letters," Cuffari wrote. "Similarly, we do not authorize our staff to sit for transcribed interviews with your committee about these ongoing matters."

Cuffari said that once "these matters are complete," his office will "consider a renewed request for documents, briefings, or transcribed interviews," according to Tuesday's letter.

CNN has requested comment from the DHS IG office.

The lawmakers also raised questions of whether Cuffari is using the ongoing criminal investigation into the missing text messages as an excuse to obstruct Congress.

"We are concerned that you are now improperly using a criminal investigation that you only recently announced to hide evidence from Congress of your misconduct and mismanagement," Maloney and Thompson said.

In his previous letter, Cuffari defended how he has informed Congress, writing to Maloney and Thompson, "consistent with the law, I have reported to Congress various access issues that my office has experienced since 2021," and cited DHS OIG's semiannual report sent to Congress in November 2021.

But, Maloney and Thompson state that the November report "made no mention of Secret Service text messages," and was given to Congress "nine months after communications were requested from the Secret Service, and long after your office learned that text messages were missing."

The committee chairs also referenced a memo obtained by the Project on Government Oversight and shared with CNN last week detailing how federal investigators believed the Secret Service was impeding them from obtaining key information about the agency's response to January 6, 2021, was significantly altered to remove reference to nearly all those efforts before a final report was presented to lawmakers in June.

Despite the alleged obstruction from Cuffari, Maloney and Thompson made a renewed request for documents and for DHS OIG personnel to be made available for interviews with a deadline of August 23.

In his August 8 letter, Cuffari indicated he would not be recusing himself, writing, "Once these matters are complete, we will consider a renewed request for documents, briefings, or transcribed interviews."

Weeks of tensions

Tuesday's letter is the latest in an ongoing back and forth between Congressional committees and DHS OIG as multiple investigations into why text messages from Secret Service agents from the days around the Capitol attack were deleted, and why it took so long for Congress to be notified are ongoing.

Maloney and Thompson say that Cuffari is also obstructing their efforts on another investigation. Since May 10, the committee chairs have been requesting documents relating to reports that Cuffari's office tried to "censor or delay" findings of domestic abuse and sexual harassment by DHS employees.

"In response to our requests, your office withheld responsive documents and instead produced a copy of a letter you previously sent to the Senate Committee on the Judiciary in response to their separate inquiry" Maloney and Thompson wrote.

Cuffari informed Maloney and Thompson that he has sought the advice of the Office of Legal Counsel "concerning whether I am permitted to release deliberative records and information to Congress."

Maloney and Thompson call Cuffari's request for the Office of Legal Counsel "highly unusual" and question whether it is a "a delay tactic meant to hamper the Committees' inquiry."

This story has been updated.