We rely entirely on voluntary contribution.

我们全靠自愿捐赠。

《牛津词典》

Most Americans advocate the spirit of social service and voluntary contribution.

大多数美国人提倡社会服务和志愿贡献的精神。

youdao

State governments maintain that the voluntary contribution of funds through state lotteries is preferable to increase state sales or income taxes.

各州政府坚持认为，通过销售彩票让居民自愿捐款以增加州内销售税或所得税的做法更可取。

youdao

It described the target as a voluntary action, and predicted it would make a "major contribution" to global efforts to deal with climate change.

VOA: standard.2009.11.26

They said they would not be following Starbucks' voluntary contribution lead.

BBC: Boris: Don't sneer at Starbucks over tax payment

It is also expected to feature a voluntary contribution from private investors, who will be invited to buy up new Greek bonds as old ones mature.

BBC: Greece: Eurozone ministers delay decision on vital loan

This review was a voluntary contribution to the BBC website.

BBC: Review: Eastern Angles' Gills Around The Green