"He is a real top bloke," he said.
Mahon said that as well as Webster being a volunteer firefighter, he would help anyone with anything - from fundraising to shifting house.
The petition states that Webster is a member of the Nelson and Stoke Fire Brigades and has been so for a few years.
"He is a very active member and as can be seen is involved in fighting the current fires - and the immigration people want to send him and his family back to England," it states.
"Everyone get behind this man. We need people like him in NZ."
The petition has so far received more than 5000 signatures, in less than 24 hours, and is addressed to Minister of Immigration Iain Lees-Galloway.
Steve and Gail Webster moved to Nelson from the United Kingdom in 2012 with their two teenage daughters.
As well as being a volunteer firefighter, the couple own Earthbloom Flower Shop in Nelson and Steve is a car salesman.
In 2016 the Nelson Weekly reported the family had their bid for permanent residency turned down in early April that year. They were told they had to be out of the country by midnight on Friday May 20.
Just 48 hours before that deadline, Steve received an email at midnight on Wednesday saying they had been given a 12-month essential skills work visa, Nelson Weekly reported.
However, Mahon said the family had again landed themselves in a fight against immigration after they had been given until June this year to leave the country.
"They have worked very hard at getting their business up and running but unfortunately it hasn't met the requirements by immigration in the timeframe," he said.
"It is a bit rough really. They give a lot to the community, have a lot of support out there, and are well liked.
"It is just not fair. Why does this always happen to the good people in life?"
Mahon said Webster's options were limited and "it's really up to people like ourselves to help support him".
"Some of the decisions coming out of immigration just make you wonder.
"I can't understand why they want to send away a family that is putting money back into the community, supporting the community and doing everything right - they are just the sort of people we need in New Zealand."
He said he was blown away by the petition's support.
"I can't believe the support we are getting. It's unbelievable to be quite truthful - I certainly didn't see it happening that quickly," Mahon said.
"It just shows you that normal, everyday Kiwis will support a cause they think is good."
Steve Webster was unavailable for comment this morning because he was stationed at the Wakefield fire.
