More than 100 Democrats from the US House of Representatives have called on the UN to take responsibility for introducing cholera to Haiti.
It is the latest twist in the allegation that UN peacekeepers unwittingly introduced the disease.
The United Nations' envoy to Haiti, Bill Clinton, has accepted UN soldiers may have brought cholera.
But with more than 7,000 deaths so far, the UN said tackling the disease is more important than attributing blame.
In a letter to the US Ambassador to the UN, Susan Rice, the 104 members of Congress stated clearly: "Cholera was brought to Haiti due to the actions of the UN."
They call on Ms Rice to pressure the UN to "confront and ultimately eliminate" the disease.
The letter says the UN should help Haiti mobilise enough money to build water and sewage systems to tackle the disease.
While members of Congress often weigh in on foreign policy issues like Iran or Israel, it is unusual for so many members to sign a letter about a small Caribbean state like Haiti.
I gathered strong circumstantial evidence that UN peacekeepers brought cholera to Haiti during a visit late last year:
- The epidemic started near a Nepalese UN base
- The UN base dumped raw sewage, which spreads the disease, near the country's main Artibonite River
- Cholera spread down the Artibonite River and into the slums of the capital Port au Prince
- Cholera was endemic in Nepal but had not been present in Haiti for a century
But UN officials shy away from taking full blame or issuing an apology.
They say tackling the disease is more important than apportioning blame.
They may also be reticent because Haitian and US lawyers are trying to sue the UN for financial compensation for the victims of cholera.