The House Intelligence Committee has released a redacted version of a whistleblower complaint at the center of Democrats’ impeachment probe of President Donald Trump.

Lawmakers began reviewing a classified version of the complaint Wednesday evening ahead of testimony Thursday morning by acting Director of National Intelligence Joseph Maguire. House Democrats who have read the document say it’s “deeply disturbing.”

The whistleblower’s identity has not been made public.

Read the full whistleblower complaint here.

The complaint is at least in part related to a July phone call between Trump and Ukrainian President Volodymyr Zelenskiy in which Trump prodded Zelenskiy to investigate Democratic political rival Joe Biden.

The White House released a rough transcript of that call Wednesday morning.