WASHINGTON — Senate Democrats threatened Thursday to block action on funding for the Homeland Security Department until Republicans jettison House-passed provisions that reverse President Obama’s key immigration policies.

Without action by Congress by Feb. 27, the department will lose a portion of its funding for counterterrorism and other activities, an event lawmakers in both parties say they want to avoid.

Republicans have vowed since last fall they would use the funding measure to reverse Obama’s recent shifts in immigration policies, and the House-passed bill is due on the Senate floor in the next few days.

But Sen. Charles Schumer, D-N.Y., said Democrats are not willing to go along, and blasted Republicans in unusually strong terms.