Payroll giving fell by £2m in 2016/17, new figures show.
Staff gave £129m through payroll giving, compared with £131m in 2015/16, according to the latest figures from HM Revenue & Customs.
The statistics, which were published on Friday and are based on information from payroll-giving agencies, show that the number of donors fell by 20,000 over the same period to just under 1.1 million.
Jacqui Abraham, client director at the Payroll Giving Team, which helps organisations to promote payroll giving, said recent political and economic uncertainty caused by events such as the vote to leave the European Union had made payroll giving less of a priority for some firms.
"If employers are uncertain about their operations, they are more likely to put payroll giving on pause," she said.
But Abraham described the figure as a "blip" against a trend of long-term growth since payroll giving began 30 years ago. "The fall is a shame, but payroll giving has become an established part of fundraising that creates sustainable long-term income," she said.
Payroll giving has generated more than £2bn since its use began. The annual sum raised peaked at £155m in 2012/13. Since then the amount has declined in three of the last four years.
A spokesman for the Charities Aid Foundation, which runs the UK's largest payroll-giving scheme, said payroll giving remained "an incredibly effective way for people to donate".
But he added: "More clearly still needs to be done to raise awareness. As part of this year’s 30th anniversary celebrations, CAF is working with employers up and down the country to help spread the word about the benefits of donating to charity in this way."