Solidarity boss Piotr Duda said the convoy would set off on Wednesday, carrying several dozen tons of food.
“Several trucks will try to get to Minsk and deliver items that may be useful in workplaces during strikes," he added.
He cautioned that he did not know whether the convoy would be allowed into Belarus.
Duda also announced the launch of a "Solidarity with Belarus" fund, into which the Polish trade union will pay PLN 1 million (EUR 227,000, USD 269,000).
"This is an amount needed for all those who lose their jobs. For their families," said Duda.
He added that Belarusians today needed support in the same way that Poles did 40 years ago.
Poland will this month mark 40 years since the Solidarity trade union and freedom movement was founded.
The rise of Solidarity marked the beginning of the end of communism in Central and Eastern Europe, and precipitated the fall of the Berlin Wall in 1989.