Greenpeace has said the oil drilling ship Noble Bob Douglas and its support vessel breached maritime protocols.
The Oil Free Seas flotilla claimed one of its boats - the Vega - was squeezed between the Noble and the Bailey Tide last night.
Steve Abel of Greenpeace said they attempted to communicate with the support boat.
"One of the most concerning aspects of this was that repeated radio calls to the Bailey Tide, asking what its intentions were, were ignored and not responded to."
Mr Abel said the incident happened at 6.10pm yesterday.