The Post Office has launched a national fit-out and refurbishment framework worth £20-£30m and split into four regional lots.
Work will include revising internal branch layouts, redecorating and installing new flooring, shop fittings, internal signage and lighting.
The refurbishment is aimed at creating open plan areas and new customer areas.
Work is split into four regions: lot a for Northern Ireland, lot b for the North Region, lot c for the Midlands and South West and lot d for London and the South East.
Procurement is due to start on 21 June and construction is expected to last two years.
Work will be undertaken as part of the crown transformation programme.