A protest over patient safety was staged outside Yorkshire Ambulance Service headquarters.
Members of the Unite union were among protesters demonstrating on Tuesday outside the headquarters at Wakefield 41 Industrial Estate, where ambulance bosses were holding a board meeting.
The union was de-recognised by the ambulance service for collective bargaining on behalf of its members in February this year in a dispute over patient safety.
The union claimed safety would be compromised by plans to send semi-skilled emergency care assistants to 999 call outs.
Last month The Express also reported claims by whistleblowers at the organisation that high-priority “red” emergencies were being downgraded to “green” to falsely meet government targets.
Yorkshire Ambulance Service (YAS) bosses have denied the claims, saying the priority of 999 calls is only altered to get to the most urgent calls on time.
Terry Cunliffe, regional officer for Unite, said: “We have turned up to make sure the board know there is a major dispute on here and that we are extremely concerned about patient safety.
“We have not been able to formally raise these matters with the trust because we have been de-recognised.”
Unite members at YAS held strike days in April and June, and talks between the two sides with the conciliation service Acas have since broken down.
YAS said in a statement: “We wholly refute the claims being made by Unite the Union and would like to stress that all of our decisions are focussed upon providing responsive, safe and high-quality care to patients in Yorkshire.
“Through Acas we continue to seek ongoing dialogue with Unite.”