Arizona Sen. John McCain is heading back to Ukraine on Thursday, leading a bipartisan group to meet with government leaders in Kiev. As the Russian occupation of Crimea continues, Crimeans are preparing to vote on a referendum on seceding from Kiev this weekend, even as the international community (and Ukraine) insist the vote is not legal.

“They’re traveling to Ukraine to show Congress’ support for the interim government and for the Ukrainian people’s aspirations for freedom, democracy and territorial integrity,” Brian Rogers, spokesman for McCain, told The Daily Beast.

It’s not the first time McCain, who has taken on the Ukrainian cause with particular relish, has visited the country. In December, he traveled to Ukraine, visiting Maidan protesters in Kiev’s main square. Those protests eventually turned violent before leading to the collapse of the government of former President Viktor Yanukovych. 

The congressional delegation will be in Ukraine until Sunday and includes Sens. Richard Durbin (D-IL), John Barrasso (R-WY), John Hoeven (R-ND), Ron Johnson (R-WI), Christopher Murphy (D-CT), Sheldon Whitehouse (D-RI), and Jeff Flake (R-AZ), who has already been tweeting about it. Many of the lawmakers are on the Senate Foreign Relations Committee.

Three Ukrainian leaders requested that the senators visit, according to Kristina Peterson and Siobhan Hughes at The Wall Street Journal. Peterson and Hughes also report that McCain has an established relationship with some of those leaders, including Vitali Klitschko, a protest leader and former world heavyweight boxer.

“They just called me and said, 'We'd like you to come out,'" Mr. McCain said, adding that the Ukrainians wanted to discuss how the U.S. could help them in “this type of crisis,” and what actions Congress could specifically take.

"I know Vitali because I'm a big boxing fan and I've known him for years," Mr. McCain said.

Sen. Whitehouse told The Daily Beast that the main purpose of the trip is to “learn more about the circumstances on the ground.” On Wednesday, Ukrainian Prime Minister Arseniy Yatsenyuk was in Washington and met with President Barack Obama.

With a vote of 14-3, the Senate Foreign Relations Committee approved legislation Wednesday that would provide aid to the new government in Ukraine, impose strict sanctions on Russia — including travel bans and denying visas on key officials — and implement controversial International Monetary Fund reforms that were a major point of contention. It now goes to a full Senate vote.