(CNN) Senate leaders are preparing for a contentious session Tuesday that could stretch several hours as well as send the chamber into a closed session as Democrats try to force the GOP into accepting witness testimony and documents to be produced during the impeachment trial, according to multiple senators and other sources familiar with the planning.

Democrats will try to amend the organizing resolution that will be offered by Senate Majority Leader Mitch McConnell. Under McConnell's plan, there is expected to be no guarantee that there will be witness testimony or documents produced, decisions Republicans want to punt until after opening arguments are completed on both sides and senators have a chance to ask questions.

But Democrats will attempt to change that. Senate Minority Leader Chuck Schumer is expected to offer at least one amendment to stipulate that witnesses must testify and that documents blocked so far by the White House be turned over to senators. But Democratic senators told CNN that it's possible Schumer could try to offer multiple amendments, and that could stretch debate on for several more hours.

That's because, at the moment, it's expected that there will be two hours of debate -- equally divided between the two parties -- for each amendment.

It's still uncertain how many amendments there would be, or precisely how Tuesday's debate would shake out because McConnell has yet to unveil his resolution publicly that will detail the procedures of the trial.

Read More