I have clients traveling to Punta Cana, DR, next week.
They have a stopover in New York. They are getting differing information about whether they need a visa.
If they are a visa required national for the United States, they will require a visa to transit via New York. This is because the US requires everybody to pass through US immigration first.
If you require a ESTA, you require a ESTA to transit if you are arriving and departing by air or sea.
I assume the nationals are Russian and Russia is on the visa required list. They will require a visa to transit.
You've not provided much information for anyone to help you with. What are the nationalities of the travelers? How long are they in New York (days? hours?) Where are they going? ("p cana" does not mean anything to me)
Here is some information on transit visas from immihelp.com:
A transit visa is also called C visa. It is your responsibility to make sure that you have the proper travel documents. Failure to obtain a transit visa, when required, may result in you being denied boarding by the airline.
If a non-US citizen is passing in immediate and continuous transit through the United States, he/she may require a valid transit C-1 visa, unless he/she is a citizen of a country that has an agreement with the United States allowing their citizens to travel to the United States without a visa or they are eligible to transit the United States without any visas under the Visa Waiver Program.