A strike on the London Underground line serving Heathrow Airport will go ahead after talks collapsed.
Members of the Rail, Maritime and Transport union on the Piccadilly Line will launch a 48-hour walkout from 12 noon on Wednesday and a five-hour strike from 8.30pm on Friday.
The union says there has been a complete breakdown of industrial relations.
Transport for London warned there will be little or no service, including the Night Tube on Friday.
The two sides met at the conciliation service Acas but talks ended without agreement.