Demonstrations, to be held in France, Canada and the US, will also coincide with the anniversary of the Paris Peace Agreement.
16 former staff members of the Cambodian Center for Human Rights alleges they were cheated out of their salaries and per diem payments.
The UN may be pushing for more funding at the tribunal, which has struggled financially all year.
The exploitation of resources, including for hydropower, have increased the burdens on some villagers.
The EU's local representative said in September his office was looking into the reports.
As a result of the charges, Sam Rainsy has been stripped of his parliamentary immunity.
The Anti-Corruption Unit have been criticized as toothless to attack the pervasive corruption across the government.
The Appeals Court said Wednesday that the two villagers could be released with time served.