Mail deliveries face delays after an unofficial strike of postal workers. Talks with union officials over the weekend failed to prevent more than 80 postal staff from walking out of two delivery centres in Oxford on Monday.
The strikes in Carterton and Witney follow the suspension of one employee and claims of bullying by another.
A spokeswoman at Royal Mail said further talks are planned with workers and an apology has been made to any customers who experience disruption.
The Communication Workers Union have confirmed they are not backing the action.
Area representatives have been in talks with postal workers at the two delivery centres concerned in an attempt to resolve the dispute.