The top Democrats in the House and Senate want President-elect Donald Trump to pledge to veto legislation that would slash Medicare and Social Security benefits.

House Minority Leader Nancy Pelosi of California and incoming Senate Minority Leader Charles E. Schumer of New York joined with Sen. Bernie Sanders, I-Vt., in a “Dear Colleague” letter that asks members of Congress to hold rallies and events on Jan. 15 (the Sunday before Trump’s inauguration) to oppose the Republican budget plan.

The budget plans of the Republican majorities in the House and Senate are likely vehicles for the GOP to repeal Obamacare, with changes to Medicare and Medicaid as a result.

“Millions of Americans voted for Donald Trump after he promised not to cut Social Security, Medicare and Medicaid. He must be held to his promises and should veto any legislation which cuts these vital and necessary health programs,” Pelosi, Sanders and Schumer wrote.

Sanders’ efforts to organize the rallies are part of his new role on Schumer’s expanded leadership team, as coordinator of outreach efforts for the Senate Democratic caucus in the 115th Congress that’s set to begin Jan. 3.

Sanders has been brought into the leadership fold after his 2016 presidential campaign yielded a large network of supporters.