Scottish Catholic International Aid Fund (SCIAF) is urging the Scottish Government to ensure its £9bn budget for the provision of goods and services is spent ethically.
Over the coming months, the Scottish Parliament will be considering the Procurement Reform Bill, which will guide how departments, agencies and public bodies make spending decisions.
SCIAF is calling on the Scottish Government to make sure that ethical, social and environmental considerations, as well as value for money, are at the heart of the Bill.
The aid agency is demanding that the Bill include clear instructions not to use the services of unethical companies who avoid paying taxes at home and abroad. The Government's spending should also be used to reduce greenhouse gas emissions and improve the lives of workers in Scotland and around the world, SCIAF said.
SCIAF is working on the campaign with a coalition of organisations, including the Scottish Trade Union Congress (STUC) and the Scottish Council for Voluntary Organisations (SCVO).
Patrick Grady, SCIAF's Advocacy Manager, said that the decisions made by British consumers "make a difference" to developing countries.
He explained: "The Scottish Government has huge purchasing power and spends around £9 billion every year on goods and services. The decisions it makes can have a really positive impact, both on the lives of workers here at home and overseas, and the environment."
Mr Grady explained that buying products which have been produced and traded ethically fairly and responsibly would allow Scotland to help millions of people.
He said: "Buying things that have been sold for a fair price and produced by companies which pay their taxes and look after their workers and the environment, means Scotland could help millions of people work their way out of poverty and reduce damage to the planet."
"We are urging people across Scotland to call on the Scottish Government to make sure that ethical, social and environmental considerations, as well as value for money, are at the heart of the new Scottish Procurement Reform Bill."
The campaign follows the announcement last week that the Scottish Government has doubled its Climate Justice Fund to £6 million to help people in developing countries cope with climate change.
The First Minister announced that an extra £3 million will be given to help reduce the impact of climate change on the world's poorest communities and provide "life-saving" support across the globe.
Philippa Bonella, SCIAF's Head of Communications and Education, welcomed the additional money for the fund at a time when developing countries are finding it harder than ever to support themselves and their families.
She said: "SCIAF projects which have received such funding are showing that by helping local communities to improve the way they farm and helping them to generate additional sources of income we can really reduce poverty and make them more resilient in the face of climate change."