According to organizations, chemical agents were also used in an attack on an Iraqi Kurdish peshmerga position on June 21 or 22.
Kurdish forces are fighting against ISIS in both Syria and Iraq where a large part has been captured by the radical group.
The type of chemical weapon is yet to be determined. None of the YPG fighters exposed to the gas had died because they were quickly taken to hospital.
The White House said it was aware of the reports of chemical weapons use and was seeking additional information.
"We continue to monitor these reports closely," Alistair Baskey, a spokesman for the White House National Security Council, said in a statement.
YPG forces have become vital for US led campaign against ISIS. YPG forces have recaptured large areas of northern Syria from ISIS.
The Syrian Observatory for Human Rights, a U.K.-based group that reports on the war using an activist network on the ground, said it had also documented the use of poison gas by ISIS in an attack on a village near Tel Brak on June 28.
ISIS's use of chemical weapons is being investigated by YPG with help from international experts from U.K. organizations Conflict Armament Research and Sahan Research.