An unofficial postal strike that is badly affecting mail services in Oxford is continuing to spread.
The latest walkout affects the OX1 and OX2 postcode areas
Workers from a third Royal Mail premises walked out on Thursday, in support of striking colleagues at the main Cowley sorting office.
Industrial action began at the sorting office more than a week ago over claims of bullying and harassment.
On Wednesday, delivery staff from Headington walked out and now staff at Royal Mail House have joined them.
The 70 delivery staff at the central Oxford delivery office are supporting colleagues they feel have been victimised for walking out over the bullying claims.
A spokesman for the Communication Workers' Union told BBC News Online the central issue of alleged bullying had been dealt with.
"The problem is that management, to express their displeasure, have insisted on an overtime ban at the Cowley centre," he said.
Royal Mail say the overtime ban is standard procedure for all staff who take part in unofficial industrial action.
"Unofficial strikes are against the law," said a company spokeswoman. "We don't feel we have any choice in the matter.
"If we didn't take action like this then we'd see this repeated elsewhere."
The latest walkout will affect mail in the OX1 and OX2 postcodes, and Royal Mail are recommending customers take mail by hand to Royal Mail House or post mail outside the affected postcode areas.