From Al Jazeera, we find out more about the letter.
Campaigners, including Noam Chomsky, the US linguist, and Naomi Klein, the Canadian author, described the debt as "patently illegitimate ... and illegal".
"The 'independence debt', which is today valued at over 17bn euros illegitimately forced a people who had won their independence in a successful slave revolt, to pay again for the freedom," the letter, published in Britain's Guardian and France's Liberation on Sunday, said.
Haiti launched a lawsuit in 2004 to recover the money, but it was abandoned after France backed the overthrow of Haiti's government.
The letter said such actions were "inappropriate responses to a demand that is morally, economically, and legally unassailable".
"In light of the urgent financial need in the country in the wake of the devastating earthquake of January 12, 2010, we urge you to pay Haiti, the world's first black republic, the restitution it is due," it said.