In summary, some University staff are taking industrial action (strike) to seek improvements to their pay and working conditions.
University staff pay conditions are negotiated nationally by UCEA. They negotiate with the trade unions on behalf of all 147 Universities including University of Brighton, and these negotiations have broken down. UCU then asked its members if they wanted to strike*. They voted in favour of strike action at 57 Universities are also now facing the same strike action. That includes University of Brighton.
Much more information can be found at https://www.ucu.org.uk/he2019
*To be legal, strike action must have a voting turnout of over 50%. (UoB had 59.21%) 76% of UoB voted in favour of the action.