People are being urged to be aware of scammers attempting to con people out of their money by posing as striking ambulance staff.
The first national ambulance strike in 30 years is planned for next Wednesday, with 10,000 ambulance workers due to join walkouts.
In a statement posted to social media, the North West Ambulance Service (NWAS) said the fraudsters are pretending to be ambulance service staff asking people for donations to cover wages lost due to strike action.
“We have been made aware that there are some people in Manchester posing as ambulance service staff and knocking on people’s doors asking for donations to pay wages whilst on strike,” the statement said.
“Please note, these people are not North West Ambulance Service staff, so please don’t donate.
“If you find their behaviour concerning, please report it to the police via 101.”
The strike action next week is over a bitter dispute over pay, with the action co-ordinated by the GMB, Unison and Unite unions.
NWAS paramedic and GMB member Paul Turner said the behaviour of the scammers was “absolutely outrageous”.
He told Sky News: “GMB is not taking part in any fundraising of this kind.
Earlier this week it emerged that military personnel would drive ambulances during the strikes, but will have to stick to the speed limit and will not be allowed to drive through red traffic lights.
Those who drive emergency vehicles will largely be restricted to non-urgent cases because of road restrictions.
Although they will be allowed to use blue lights and sirens, they will have to follow normal driving rules.
This means they will not be able to break the speed limit or jump red lights.
A health minister said some less urgent 999 callers will get a taxi instead an ambulance turning up at their door during the strike.
Will Quince told MPs: "999 calls are triaged and categorised from category 1 to category 4. On the days of ambulance strike action it’s likely that category 1 and category 2 calls, where there is an immediate threat to life, will be responded to.
"And we are looking at ways in which we can provide additional support for category 3 and category 4 including things like block booking taxis and things like support through community healthcare and local authorities and community support.”
Ministers held an emergency Cobra meeting earlier this week to discuss plans for military staff and civil servants to cover for striking workers in the coming weeks.
