Facebook has seen a flurry of check-ins to the Standing Rock Indian Reservation, which is at the centre of a protest against the Dakota Access Pipeline.
The check-ins appear to be a reaction to a Facebook post which claims police are using the social media giant to monitor protesters trying to block the construction of the oil pipeline in North Dakota.
The post urges people who support the protest to virtually check into the site, to confuse authorities.
Morton County sheriff’s department fired back with a post of its own on Monday, calling the post’s claim “absolutely false”.
The main camp supporting the protest said the check-ins had brought welcome publicity to the cause, but also urged supporters to take “physical action” as well.
More than 140 people were arrested at the construction site over the weekend.
Demonstrators have been camping for months in an effort to block the 1,900km pipeline, which will span four states.