A charity says it is losing out on thousands of pounds worth of donations to rag trade collectors.
Bedfordshire-based Keech Hospice Care said donations to its charity shops had plunged because of increases in house-to-house collections from unscrupulous collectors.
Keech's retail manager Philip Kojcinovic said he believed the charity was losing as much as £5,000 a week.
It has 17 shops across Bedfordshire, Hertfordshire and Milton Keynes.
The charity raises money for its adult and children's hospice service.
Mr Kojcinovic said: "Rag trade collectors are putting sacks through people's doors, paying only nominal amounts to the charities whose branding they use."
The charity's chief executive Mike Keel, said: "It's a significant amount of money for us to be losing.
"We have to raise £5m a year to keep our services going. Times are tough at the moment, the recession is affecting everybody, but patients don't stop being sick and we have to raise as much money as we can from our charity shops.
"People often believe that the bags that come through their front door are for charities, and that's not always the case.
"We want people to be aware that they're not always giving to charity when they put unwanted belongings into these bags and leave them out for collection - they have to read the small print," said Mr Keel.
A spokesperson from the British Heart Foundation said it was not just small charities that were being affected.
They said: "The problem is on the rise. In 2008/09 we lost £1.2 million, in 2009/2010 £3 million and with a further 18% drop in household collection returns since April 2010, we expect to lose more than £3 million this current financial year - money which could be spent in the fight against heart disease."
Clothes Aid is the UK's leading clothing collection agent with more than 10 years of experience in door-to-door fundraising.
They are a fully-licensed fundraiser complying with all UK Charity Commission regulations concerning the collection and sale of used clothing.
"We collect unwanted clothing and textiles on behalf of our charity partners all across the UK. Our experience and hard work has helped us raise to date £3.15m for UK charities and NHS trusts," said a spokesperson.
"For every tonne of clothes, shoes and bedding collected, our partner charities receive at least £50. Each charity is guaranteed a minimum annual amount from Clothes Aid. Our service thus provides a steady revenue stream, leaving the charities to concentrate on their important work whilst Clothes Aid delivers the funds."
Clothes Aid has joined the Charity Commission and The Department for Social Development (DSD) to produce a guide to help householders deal with doorstep charity collectors.
Rosie Chapman, the Charity Commission's Director of Policy and Effectiveness, said: "With the current pandemic of 'charity' clothes and donated goods collections sweeping the UK, it's more important than ever that people are armed with the pointers they need to decide whether they want a charity to benefit from their generosity. We hope this joined-up guidance will, for the first time, provide UK householders everywhere with the information they need to make these choices."