SEATTLE (AP) — Several U.S. tribal leaders are voicing opposition to a proposed pipeline expansion project that would increase tanker traffic in the waters of Washington state and Canada.

Leaders from four Native tribes are in Victoria, B.C., to testify before Canada’s National Energy Board today (Wednesday).

The contentious Trans Mountain pipeline expansion project would nearly triple the flow of oil from the Alberta oil sands to the Pacific Coast.

Tribal leaders say increased marine shipping through the Salish Sea will harm endangered southern resident killer whales, natural resources and their cultural way of life.