Post Office managers will stage industrial action tomorrow for the first time in over three decades in a bid to break a 16-month pay freeze.

Unite revealed yesterday that its 900 managers in high-street shops and the company's headquarters will carry out an overtime ban and work to rule.

Members have voted to reject a non-pensionable cash bung from bosses and take action for the first time since 1979 to win a fair pay rise.

And national officer Brian Scott warned Post Office leaders they must "get their skates" on and negotiate to avoid further industrial action.

"Unite members will not undertake any overtime, will refuse to work any additional hours or do work not proper to their role in the organisation," he said.

"This is an important day for Unite members in the Post Office. They are keen to impress upon their employer their dissatisfaction with the failure to reach a pay agreement with the union and see this an opportunity to protest."

Mr Scott blamed the "intransigence" shown by bosses since June 2012 for forcing tomorrow's action, which will also see managers refusing to work outside their designated office.

That is a boost to the 4,000 members of the Communication Workers Union in Crown offices campaigning to win their first pay rise since April 2011.

They have already staged 12 days of strike action over the dispute this year and Unite's announcement will pile added pressure on bosses to deliver a deal.