The Salvation Army is paying $600,000 a year in tip fees to dispose of rubbish left outside its 125 family stores nationwide.
Workers at Wellington region shops said the problem was worse as Christmas approached.
One said used condoms, dirty nappies and clothes stained with faeces had been left outside her shop.
Salvation Army lower North Island family store manager Gareth Marshall said dealing with unwanted "donations" left outside the 26 stores under his control was a "frustrating, significant issue for store staff".
He said the $600,000 paid in tip fees was money the army would prefer to give needy families.
"People who abuse us will abuse us, no matter what. We are still very grateful for everything we get," he said.
Stores were open six days a week with signs on doors asking people not to leave goods when the shops were closed.
There was also a significant pilfering problem. By the time staff arrived for work, particularly on Monday mornings, their first job involved cleaning up large piles of rubbish picked through by overnight pilferers.
"Staff become very frustrated when unwanted rubbish is left outside shops overnight and at weekends," Mr Marshall said.
The army's stores make about $10 million a year from selling secondhand goods such as furniture, household goods, toys and books.
Karori resident Chris Myers said the area outside the shop often looked like a "tip site" at weekends.
"People are taking the good stuff and dumping the rubbish. It's very sad," she said.
John Rossbotham, manager of the Catholic Church's six St Vincent de Paul shops in Wellington, said loading up a van and travelling to the tip on Monday mornings was part of the "cost of doing business".
He sympathised with the Salvation Army, but said "Vinnies" shops in Newtown, Miramar, Island Bay, Aro St, Johnsonville and Khandallah rarely had "donations" of household rubbish outside trading hours.
- The Dominion Post
How excited are you about the 2014 Commonwealth Games?Related story: After the hype, time to let the Games begin