In a letter sent to Zelensky on Wednesday, Johnson pressed the Ukrainian president to “immediately fire” Ambassador Oksana Markarova after she organized a trip to an ammunition plant in Scranton, Pennsylvania, and was accompanied by only Democratic officials. Republicans have since accused Zelensky of election interference, raising questions about whether U.S. taxpayer dollars were used to fund the trip in violation of federal law. 

“The tour was clearly a partisan campaign event designed to help Democrats and is clearly election interference,” Johnson wrote. “This shortsighted and intentionally political move has caused Republicans to lose trust in Ambassador Markarova’s ability to fairly and effectively serve as a diplomat in this country. She should be removed from her post immediately.”

Johnson reiterated calls for “all foreign nations” to avoid weighing in on the presidential election, telling Zelensky that his relationship with the U.S. becomes “unnecessarily tested and needlessly tarnished” when Republican candidates become targeted by Ukrainian officials. The letter comes just one day before Zelensky is set to visit Capitol Hill and meet with lawmakers in both the House and Senate.

The letter directly responds to Zelensky’s visit to Pennsylvania earlier this week, specifically his comments suggesting a Trump-Vance administration could lead to “global conflict.” Zelensky also angered Republicans when he told the New Yorker that Sen. J.D. Vance (R-OH), Republican vice presidential nominee, was “too radical” and that former President Donald Trump, Republican presidential nominee, “doesn’t really know how to stop the war even if he might think he knows how.”

The comments have sparked outrage as Republicans argue the remarks may amount to foreign election interference. 

Lawmakers have also pushed for an investigation into whether there was “any direct or indirect coordination” between Zelensky’s visit and any political campaigns, specifically pointing to the fact only Democratic officials were present for the Ukrainian president’s stop in Pennsylvania. Those who accompanied Zelensky include Gov. Josh Shapiro (D-PA), Sen. Bob Casey (D-PA), and Rep. Matt Cartwright (D-PA).

House Republicans have specifically requested a full accounting of the use of military aircraft and Secret Service resources, including an explanation of the justification for those resources and how it “aligns with U.S. national interests.” Additionally, lawmakers have requested an accounting of all other uses of taxpayer funds in connection with Zelensky’s visit. 

A group of House Republicans have pressed the Justice Department to open an investigation, and the House Oversight Committee announced Wednesday it would be opening its own inquiry into the matter. 

The committee sent letters to White House counsel Edward Siskel, Defense Secretary Lloyd Austin, and Attorney General Merrick Garland. In the letter to Siskel, Comer said the “apparent campaign event” may have resulted in the “potential interference in a federal election.”

Chairman James Comer (R-KY) is requesting any information, both internal and external, regarding Zelensky’s visit to the U.S. to be delivered to the committee no later than Oct. 2.