House Homeland Security Committee Chairman Bennie Thompson (D-Miss.) criticized Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenDHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections Democrats smell blood with new DHS whistleblower complaint MORE on Tuesday for declining to testify before the panel.

Thompson wrote to Nielsen, indicating she had refused to appear before the committee on Feb. 6 to discuss border security. The Mississippi Democrat called her decision "unreasonable and unacceptable."

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"Your attempt to use the President’s recent shutdown as an excuse not to testify before Congress prior to the impending shutdown is outrageous," he wrote. "As Secretary of Homeland Security, you should be prepared to testify on border security, the very issue that caused the recent shutdown, at any time and certainly prior to the potential February 15 lapse in appropriations."

Nielsen has echoed President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE's calls for increased security along the southern border, including a wall. Trump's demand for $5.7 billion to build a border wall was at the center of a stalemate over the partial government shutdown that lasted 35 days.

Trump signed legislation last week that funded the government for three weeks and did not include wall funding. It provided for a group of bipartisan lawmakers to negotiate border security funding and come up with a proposal prior to the next funding lapse on Feb. 15.

In Tuesday's letter, Thompson noted that Nielsen publicly pressed for wall funding and increased border security during the shutdown, and suggested her input is needed for Congress to negotiate moving forward.

"In your public comments on border security, you maintained that Congress should 'get [its] job done,' " Thompson wrote. "Please know that as Chairman, I intend to ensure the Committee fulfills its oversight responsibilities on this important matter."

#BREAKING: Chairman @BennieGThompson just sent a letter to @DHSgov Sec Nielsen on her refusal to come before Congress & testify on border security.



It’s time for the Admin to realize that things have changed.



Real, necessary, Congressional oversight has arrived. pic.twitter.com/53Fhfzgjht — House Homeland Security Committee (@HomelandDems) January 29, 2019

Thompson, who took over as chairman of the House Homeland Security Committee at the start of the new Congress, invited Nielsen earlier this month to testify on border security.

Department of Homeland Security spokesman Tyler Houlton accused Thompson of sending a "misleading letter," insisting that Nielsen had accepted the invitation to testify but proposed alternative dates in February.

“Unfortunately, instead of calling the Department or reaching out to the Secretary to identify a mutually workable alternative date, the Chairman chose to release a letter falsely claiming the Secretary was refusing to testify," Houlton said in a statement. "Such missives are unproductive and unhelpful in sustaining comity between the Committee and the Department.

"The Secretary respects the important role of Congressional oversight and looks forward to working with the Committee on important homeland security issues," he added.

Nielsen most recently testified before Congress at a House Judiciary Committee hearing in late December.

--This report was updated at 11:29 a.m.