Police were called to campaigners holding a candle-lit vigil outside Chorley and South Ribble District General Hospital on Wednesday night.
Around 40 people had gathered to thank acute doctors and nurses for reopening the department nine months after it was closed in April last year.
They were delivering a card and cake to A&E staff.
Andrew Birchall of Protect Chorley Hospital from Cuts and Privatisation said: “We were ordered off what they said is private land.”
Karen Partington, chief executive at Lancashire Teaching Hospitals NHS Foundation Trust said the gift of the cake was a “thoughtful gesture” but added: “The protestors were blocking pavements, and were congregating in front of ambulance bays. As this was a clear risk to safety they were politely asked to leave by managers, nursing staff and finally security. However the majority remained and refused to leave. The police were subsequently called to ensure the safety of protestors, patients, visitors, staff, and arriving ambulances.”