The hoodies began in Newquay, but have spread around the South West
Hundreds of people are supporting a move to ban the sale of replica lifeguard sweatshirts.
The red hoodies emblazoned with "Lifeguard" have exploded in popularity around South West seaside resorts.
But campaigners, as well as the RNLI, fear tourists might mistake those wearing them for real lifeguards.
Matthew Perry, of Hayle Surf Lifesaving Club in Cornwall, has nearly 2,000 supporters of his internet campaign to discourage shops selling the garments.
Mr Perry, who is organising a petition to give to Restormel Borough Council, said: "I have seen adults walking along the beach together wearing these hoodies.
"Sometimes they even try to get their picture taken with the rescue equipment.
"But impersonating someone who is trained to save lives costs lives."
The hoodies and t-shirts in the red and yellow colours of the RNLI lifeguards have been selling in Cornwall for the last five years.
The red and yellow colours are recognised around the world
This year their popularity has spread and they have been seen in Devon resorts.
Steve Instance, RNLI Lifeguards inspector for the South West, said the fake goods presented a "massive" problem because the red and yellow lifeguard colours were recognised globally.
He said: "If you were in a panic you could be easily misled by these garments."
But Daniel Pettit, manager of No Worries surf shop in Newquay said: "I'm not going to stop selling them.
"We have been making these t-shirts and hoodies for years and they don't say RNLI on them."
He added: "The credit crunch means you have a choice, either go bankrupt or supply people with what they want.