The Republican Speaker of the U.S. House of Representatives demanded on Wednesday that Ukrainian President Volodymyr Zelenskyy fire his ambassador to the United States over Zelenskyy’s trip this week to a factory in Pennsylvania.

“I demand that you immediately fire Ukraine’s Ambassador to the United States, Oksana Markarova,” Speaker Mike Johnson wrote in a letter to Zelenskyy.

Johnson released the letter a day before Zelenskyy was due to visit the U.S. Capitol in Washington for meetings with lawmakers. Johnson was not expected to meet with the Ukrainian leader.

The Ukrainian Embassy in Washington did not immediately respond to a request for comment.

Some Republicans have been fuming over Zelenskyy’s visit earlier in his weeklong trip to the United States to an ammunition plant in President Joe Biden’s hometown of Scranton, Pennsylvania. Pennsylvania is one of the swing states seen as crucial to victory in the November 5 presidential election.

During the trip, Zelenskyy also met with Pennsylvania Governor Josh Shapiro, Senator Bob Casey and U.S. Representative Matt Cartwright, who are all Democrats.

Biden’s vice president, Kamala Harris, is the Democratic candidate running against Republican former President Donald Trump in the race for the White House.

“The facility was in a politically contested battleground state, was led by a top political surrogate for Kamala Harris, and failed to include a single Republican because — on purpose — no Republicans were invited,” Johnson wrote.

“The tour was clearly a partisan campaign event designed to help Democrats and is clearly election interference,” he said.

The Republican-led House Oversight Committee had already announced that it would investigate whether Zelenskyy’s trip was an attempt to use a foreign leader to benefit Harris’ campaign.

It is common practice for governors to meet with foreign leaders who travel to their states. In July, Zelenskyy visited a factory in Utah and was hosted by that state’s Republican governor, Spencer Cox.