Elegran
Don't unions have phones, email accounts and internet access with advertising and marketing possibilities? If a business can keep in touch with workers in their own homes, surely unions can? The home-office workers can also contact their union online if they have any concerns about their working conditions - assuming that their union representatives have made themselves known to them and have been seen to be approachable.
The unions have used online recruitment for many years. However, still the major percentage of recruitment is carried out by activists in workplaces speaking to new employees and encouraging them to join especially when they perceive problems in their employment.
White-collar employees working from home will not affect Unite and some other large unions as they in the main represent manual workers.
However, the GMB could be destroyed by widespread home working and they are right-wing in their political views and very much supporters of Starmer in his troubled relationship with Unite and the Rail Unions.
The above will make the Labour Party ever more dependent on the large very left-wing unions for their funding and I am sure there are many who claim to be supporters of the Labour Party on this forum who would certainly not wish to see that.