"Beginning in January, it is likely that Republican leaders will follow through on their threats to ram through a budget bill that will severely undermine the health care needs of the American people," the letter read.
Republicans are planning to use a procedural maneuver known as budget reconciliation to repeal the law with a simple majority vote in the Senate as soon as January, but Democrats are trying to lay the groundwork for a grassroots movement against the repeal.
Democrats argue that repealing the law will take away insurance for more than 20 million people and take away Medicaid expansion in states throughout the country. Republicans say their plan wouldn't phase out Obamacare for two to three years. Republicans also promise they will replace it, but have yet to come up with a replacement bill.
In the letter, Schumer, Pelosi and Sanders designated Jan. 15 the day of action and asked activists to "organize a rally or other event" back in the states. Democrats are calling Jan. 15, "Our first stand. Save health care."
The letter also demanded that President-elect Donal Trump not touch or make changes to Medicare or social security, programs he vowed not to mess with on the campaign trail.
"He must be held to his promises and should veto any legislation which cuts these vital and necessary health programs," the letter readx.