U.S. Energy Secretary Rick Perry recommended Ukraine President Volodymyr Zelenskiy’s administration talk with Daniel Yergin, a Pulitzer Prize winning energy historian, and Carlos Pascual, a former ambassador to Ukraine, on energy reforms, an U.S. Energy Department official said on Monday.

Perry also recommended Zelenskiy’s administration talk to industry experts including Texas businessmen Michael Bleyzer, a Ukrainian-American, and Robert Bensh, a frequent visitor to Ukraine, as well as unnamed Energy Department experts on a visit in May for the inauguration the Ukraine president, the official said on condition of anonymity.

Perry attended Zelenskiy’s inauguration as a last minute replacement for U.S. Vice President Mike Pence.

The visit has drawn scrutiny as Democrats in the U.S. House have requested documents related to Perry’s activities in Ukraine as part of their impeachment investigation of President Donald Trump. Perry himself has not been subpoenaed.