Macmillan Cancer Relief's annual coffee morning event will be promoted on 30 million milk cartons as part of a partnership with Dairygate.
Dairygate, the Co-operative Milk Association's fresh milk brand, will print information about the event on cartons which will be distributed to retailers, cash and carriers, food service outlets and schools and universities.
The World's Biggest Coffee Morning aims to raise more than £3.5 million to support people living with cancer. It is the first time that Macmillan has struck a corporate deal that has resulted in an on-pack promotion.
"Although we've had a lot of corporate support for our coffee mornings, this is the first time that we're able to get information out to the general public in this way,
said Jenny Edwards, head of events at Macmillan.
"This is a fantastic way to spread the message to a wide audience, and we're keen to try and secure this kind of distribution with future partnerships."