US Secretary of State Mike Pompeo has been subpoenaed.
A Democratic-led US House of Representatives committee issued the order on Friday.
They want to him to hand over documents regarding contact the US government had with the Ukrainian government.
Earlier this week House Speaker Nancy Pelosi launched a congressional impeachment inquiry of US President Donald Trump.

Shooting at Australia's Bondi Beach kills 12
Police hold person of interest after Brown University shooting leaves two dead
Hamas says Israel's killing of senior commander threatens ceasefire
Ukraine's Zelenskyy ditches NATO ambition ahead of peace talks
Thailand declares curfew along coast as Cambodia border fighting spreads
India tightens pollution curbs as Delhi's air quality worsens
'Peace is not far away' says Erdogan after Putin meeting
Belarus frees Nobel winner, protest figures as US lifts more sanctions
