Lincoln County Hospital has declared it is in crisis mode once again with some patients waiting up to 19 hours in A&E.
Bosses have blamed a huge surge in demand.
United Lincolnshire Hospitals NHS Trust also declared a critical incident at Boston Pilgrim, where patients waited 21 hours in A&E.
It is the third time in as many months that the hospital has warned about a sudden and significant increase in patients.
UNISON East Midlands regional organiser Elliot Dean said: “The trust’s declaration of a critical incident shows services are underfunded and overstretched across Lincolnshire and winter pressures will only make this worse.
“Healthcare staff across the county are working extremely hard to deliver the best possible patient care in incredibly challenging circumstances.
“However the closure of the Lincoln walk-in centre, lack of GPs in the county and the downgrading of A&E services at Grantham Hospital are all increasing demand at Lincoln and Pilgrim Hospital A&E departments.
“It’s vital the government recognises this crisis and takes urgent action to put funding in place to invest properly in all NHS services to ensure a high quality health system for the residents of Lincolnshire.”
Back in November, the former Lincoln MP Karen Lee said the situation at A&E was the “worst my contact has seen” with waiting times up to 20 hours.
Former staff at Lincoln County Hospital previously spoke out about problems of safety and understaffing, which they claim were flagged up but never addressed.
Concerns included staffing levels, as well as newly qualified doctors being left unsupported and overwhelmed by their workload.