Half a million people were left exposed by the cyber attack on BA's systems last year last year and BA could face a record fine for their “poor security arrangements”.
At a hearing at the High Court in London, Mr Justice Warby granted a group litigation order, paving the way for a mass legal action.
Personal details, including payment data and addresses, were compromised by the hack, according to the Information Commissioner's Office.
Part of the scam involved passengers being diverted to a fake website, through which their details were harvested by the attackers.
The airline informed the ICO and began to contact affected customers when it discovered the breach in September 2018.
There are currently more than 5,000 affected customers being represented by SPG Law and a further 230 represented by Your Lawyers Limited, who are bringing claims for compensation.
But the potential number of claimants is much larger and the judge granted a window of 15 months from the hearing on Friday for people to join the group litigation.
Aman Johal, director of Your Lawyers, said: "Today's grant of a group litigation order is a key step towards justice for the hundreds of thousands of victims of the British Airways data breach scandal."
The ICO announced in July this year its intention to impose a record fine of more than £183 million on BA over the breach, which is believed to have started in June 2018.
A spokesman for the watchdog said at the time that the proposed fine would be the largest it has handed out and the first to be made public since new data laws came into force.
The General Data Protection Regulation (GDPR) came into force in May last year and means firms can be fined up to 4% of annual turnover for data breaches.
The proposed fine represents 1.5% of BA's annual turnover.
The ICO's investigation found that a variety of information was compromised by "poor security arrangements", including log in, payment card and travel booking details as well as customers' names and addresses.
In a statement after the fine was announced, Information Commissioner Elizabeth Denham said: "People's personal data is just that - personal.
"When an organisation fails to protect it from loss, damage or theft it is more than an inconvenience.
"That's why the law is clear - when you are entrusted with personal data you must look after it.
"Those that don't will face scrutiny from my office to check they have taken appropriate steps to protect fundamental privacy rights."
Alex Cruz, British Airways' chairman and chief executive, said at the time that the airline was "surprised and disappointed" in the ICO's initial finding.
"British Airways responded quickly to a criminal act to steal customers' data.
"We have found no evidence of fraud/fraudulent activity on accounts linked to the theft.
"We apologise to our customers for any inconvenience this event caused."