The Biden administration is deeply concerned over corruption within Ukraine’s government and business sectors, according to documents obtained by Politico.

The Biden administration is pleading with Ukraine to root out corruption within its highest ranks and warns that already-strained western support will further decrease it if it doesn’t address the issue, Politico reported on Monday. The fears of corruption outlined in the private document are much more severe than the Biden administration has admitted publicly as it struggles to rally continued support for Ukraine’s war effort against Russia.

“Perceptions of high-level corruption… [could] undermine the Ukrainian public’s and foreign leaders’ confidence in the war-time government,” according to the documents obtained by Politico.