Four people have been arrested over offences relating to animal rights extremist activities.
Officers from Humberside and West Yorkshire Police carried out a planned joint operation on Tuesday.
Two women, aged 56 and 30, were held in Preston, east Yorkshire. A boy aged 17, from Leeds, and a 27-year-old man, from Shipley, were held in West Yorkshire.
They are accused of intimidating businesses into stopping contracts with organisations that do animal research.
Undisclosed items were seized during searches at several properties under the Serious Organised Crime and Police Act 2005.
All four people are being questioned at police stations in Hull.