Stores could introduce "fitting fees" because increasing numbers of people are trying on their clothes then looking for something cheaper online.
Sports shoes are one of the most popular items to buy online because they're often cheaper, says the New Zealand Retailers' Association.
Chief executive John Albertson said many retailers had noticed the practice of trying without buying.
"If it happens to any extent, it's wrong because you're crossing that line," he said.
"You're getting somebody to put a lot of work and effort into something and they let you try something on and then you buy somewhere else. There's a moral question about that."
And while Mr Albertson said he wouldn't advocate fitting fees, he can understand why retailers would charge them.
"I think it would very much be a last resort. If you have somebody in your store, you have the opportunity to get a sale."
About a billion dollars a year was spent through overseas websites.
Mr Albertson said that when people bought from overseas sites, they lost the protection of the Consumer Guarantees Act.
Rebel Sport's managing director Rod Duke said he had no doubt that people were trying on goods in their stores before buying online but it wasn't affecting the business.
Mr Duke said he could imagine some retailers contemplating introducing fitting fees, but rejected the policy himself. "I would never, ever, ever contemplate that."
Eleisha Balmer, spokeswoman for Kiwi label Ruby, said more than 50 per cent of people who walked through its doors had seen the clothes online - on blogs or social media - and went to the stores to try them on and buy them there.
Rumours in the Australian retail industry that companies would introduce fitting fees had led people to thinking the problem was worse than it is, said the Australian Centre for Retail Studies.
Research by the centre found 4 per cent of shoppers tried in store before buying cheaper online.
Most of those people - 61 per cent - did not intend to purchase online at first, but found the product they were looking for was not available in stores.
Shopper gets best of both worlds
When Georgia Harmos comes across a pair of shoes she likes online, she sometimes pops out to a shop that stocks them to make sure they fit.
Once satisfied that they're the pair for her, the 20-year-old then buys the shoes - usually heels - online.
"They're so much more expensive in the store and you can get them for so much cheaper online. You can go in and see them in real life and see what size you'd be," she said.
Miss Harmos, a music and marketing student at Otago University, said that at most she'd buy something online once a week, though it was more likely to be once a fortnight.
"I find it a lot easier to compare prices between sites and there's a way bigger variety.
"Here it's so much more expensive and everyone has the same stuff."
Some of her favourite sites include ASOS, Top Shop and Solestruck.
Miss Harmos, of Remuera, still enjoys hitting the streets to go shopping, but says it's more of a social activity.