Campaigners are calling for clearer labelling on charity clothes collection bags amid fears that charities may be missing out on donations.
Pensioners Forum Wales said elderly people often found it hard to tell between charity bags posted through their door and private firms' bags.
The group said some wanting to donate to charity were unwittingly lining the pockets of private companies.
The Charities Commission said it had issued advice on identifying bags.
The collection bags in question are those posted through domestic letterboxes which ask for householders to fill them with their unwanted clothes and textiles.
Some are sent by charities but others are sent by firms which sell the donated goods for profit.
Nancy Davies, chair of Pensioners Forum Wales said the problem stemmed from charities using very small lettering to print their registered charity number on collection bags.
Private companies also use small print for their company registration numbers, she explained.
"It can be difficult, at first glance and especially for people with poor eyesight to tell the difference between charity collection bags and those that private companies post through their door," said Ms Davies.
"Pensioners Forum Wales is worried that people who think they are donating their goods to charities are unwittingly lining the pockets of private companies, while charities are missing out on much-needed funds.
"This is why it is so important that charity collection bags have clearer labelling on them so that it is easier for members of the public to tell who is going to benefit from their donated goods."
Eileen Kinsman of the Welsh Council for Voluntary Action (WCVA) commented: "Legitimate charitable door-to-door clothing collections raise significant funds for charity which is under threat from bogus collectors."
Ms Kinsman said the Institute of Fundraising (in conjunction with the Fundraising Standards Board, the Textile Recycling Association, the Charity Retail Association and Kidney Research UK) had produced guidance on house-to-house clothing collections including tips on how to spot bogus collections.
"As well as raising significant sums for charity, door to door clothing collections are good for the environment and popular with the public because they are convenient to use," said Ms Klinsman.
Steve Jones of Wales Heads of Trading Standards said it was "concerned" about the issue and sympathetic with the fears expressed by Pensioners Forum Wales.
"We acknowledge that it's not always straightforward to tell the difference between collection bags," he said.
"If there's any doubt at all as to whether you are giving to a genuine charity then don't give. Give instead to a local charity shop."
The Charity Commission, the independent regulator of charities for England and Wales, said it has issued warnings against bogus clothing collections, and advice on how to ensure donations go to a genuine charity.
The charity said: "The commission has received a number of calls recently from people who have been given misleading leaflets which suggest that the proceeds of a clothing collection will go to charity or charitable causes when in fact they benefit a private business or individual.
"The commission is also aware of recent cases where fraudsters have used the name, logo and charity registration number of a genuine charity to appeal for donations and keep the profits.
"Most collections for charities are genuine and provide them with an important source of income.
"People should not be discouraged from donating to collections carried out by genuine charities to raise funds for a legitimate charitable cause."