Washington (CNN) Senate Democratic leader Chuck Schumer sought to turn up the pressure Monday on Senate Majority Leader Mitch McConnell and Senate Republicans by outlining a plan for how he wants Republicans to investigate a whistleblower complaint that has sent shockwaves through Washington.

In a letter to McConnell on Monday, Schumer writes that he is calling on the majority leader and Senate Republicans who control the chamber to "take immediate action to stop President Trump from withholding an Intelligence Community whistleblower complaint that by law must be transmitted to Congress, and to begin an investigation into the Administration's handling of security assistance to Ukraine."

Schumer calls for hearings "to determine exactly what prompted the whistleblower to file this urgent complaint," and says they should feature testimony from a host of administration officials, including acting Director of National Intelligence Joseph Maguire and Secretary of State Mike Pompeo. Schumer also calls for testimony from Trump's private attorney Rudy Giuliani.

Schumer also states that a subpoena should be issued "to compel the delivery of the whistleblower complaint to Congress, as required by law."

The letter is the latest effort by congressional Democratic leaders to push for an investigation into the whistleblower complaint amid a controversy surrounding Trump and his contact with Ukraine.

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