Kate Nicholls, chief executive of industry group UK Hospitality, warned tourism and leisure businesses were already fragile after pandemic lockdowns and would take a ‘big hit’.
Rail travel to and from Portsmouth will be severely impacted due to the strikes.
The Rail, Maritime and Transport union (RMT) confirmed industrial action would go ahead on next Tuesday, Thursday and Saturday.
Speaking to Times Radio, Ms Nicholls said: ‘At the best, we think it’s going to take a hit to hospitality revenues of over half a billion pounds.
‘But that presupposes that many people will travel on those shoulder days when the trains and the Tubes will still be disrupted – it could be more significant than that.
‘And if you look across the whole tourism, and leisure and theatre industries as a whole, you are definitely looking at an economic hit of over a billion pounds.’
Ms Nicholls added that tourism and hospitality businesses had already been damaged by the cost-of-living crisis and urged the Government, rail networks and the RMT to reach an agreement.
The dispute is over the standard of pay, staff shortages, and working conditions.
General secretary Mick Lynch, of RMT, said: ‘Despite the best efforts of our negotiators no viable settlements to the disputes have been created.’
Network Rail and 13 train operators will proceed with the strikes.
The action by tens of thousands of rail workers will cripple services for most of the week.
Mr Lynch added that thousands of jobs were being cut across the rail networks and workers were facing below-inflation pay rises.
‘In the face of this massive attack on our people the RMT cannot be passive’, he said.
‘So today, having heard the reports on the discussions that have been taking place we are confirming that the strike action scheduled to take place on June 21, 23, and 25, will go ahead.
‘We want a transport system that operates for the benefit of the people, for the needs of society and our environment – not for private profit.
‘We call on the entire labour movement and the working people to rally to the support of the RMT and our members in this struggle.’