Sharing the Caring, the payroll giving agency owned by Help the Aged, is to merge with the Charities Aid Foundation.
Sharing the Caring raises about £6m a year from corporate clients for the charity sector as a whole through payroll giving services, but only ever delivered a modest return to Help the Aged, a spokesman said.
A "small number" of the 41 employees at Sharing the Caring will lose their jobs.
The merger comes as CAF figures showed an increase in payroll giving to £91m in 2003/4, compared with £86m in the previous year.
CAF paid no money to Help the Aged for the transfer of the service, and the charity denied that the merger had anything to do with previous income shortfalls.
The spokesman said that action had been taken to resolve Help the Aged's £6m deficit last year and it "was no longer an issue".
Sharing the Caring will continue to operate from its Canterbury location, but will move offices, following consultation, when the lease runs out next September.
Jenny Byers, executive director of donor services at CAF, said: "By mobilising the combined reach and expertise of Sharing the Caring and CAF, we can generate even more interest in this form of giving."