A group called the Mi'kmaq Warriors Society and people from various Cape Breton reserves started a protest Thursday against oil and gas exploration on the island.
The 20 protesters say they want to draw attention to the dangers involved with the work.
One company planning to do work on the island is PetroWorth Resources Inc., which is supposed to start oil exploration work near Lake Ainslie later this year.
Protesters say no oil and gas development can be done safely and the work threatens the health of people on the island, including those living in aboriginal communities.
The demonstrators aren't saying how long they'll stay near the Causeway or if they'll disrupt traffic.
RCMP were on the scene Thursday and said they'd spoken with the organizers and will keep an eye on the protest to make sure it remains peaceful.