The Koch brothers are getting in the way of a Senate package to aid Ukraine, Majority Leader Harry Reid said Thursday.

“The Koch brothers continue to hold up the situation we have in Ukraine,” the Nevada Democrat said, according to Politico.

Support for the Ukraine aid legislation, which would also reform the International Monetary Fund, is being used as a trade-off for a “delay in IRS rules changes affecting the political activities of nonprofits,” according to the report.

The Internal Revenue Service regulation changes would impact the activities of nonprofits such as Americans for Prosperity. AFP is backed by the Koch brothers, and the group plans to continue flexing its financial muscle in campaigns across the country.

The Senate Foreign Relations Committee passed along a Ukraine aid bill on Wednesday, but House Majority Leader Eric Cantor called for a vote on the House version instead.

The IRS reforms are opposed by many House Republicans, which may put at risk an assistance package for Ukraine. The nation has weathered violent protests and a power struggle with Russia for control of its Crimea region.