A union has claimed more than 30 UK staff of Rockstar Games – the developers of Grand Theft Auto – have been sacked in a “union-busting” move by bosses.

The Independent Workers’ Union of Great Britain (IWGB) has said it appears that staff at the company’s base in Edinburgh had been sacked for “trade union activity” and claimed that the dismissals were “unlawful and retaliatory”.

The union said that all of the workers affected had been members of the union and of a chat group on the Discord app.

Grand Theft Auto (GTA), created by Rockstar Games which is a subsidiary of Take Two Interactive, has been the most profitable videogame franchise in the world with GTA 5 having generated more than 8.0 billion US dollars (£6 billion) in revenue since 2013.

Take Two Interactive has said the workers were dismissed for “gross misconduct”.

The IWGB said in a statement: “Over 30 members of UK staff at Rockstar Games, developers of the Grand Theft Auto series, were fired on Thursday October 30 due to trade union activity.

“The staff, who were all part of a private trade union Discord channel and members of the Independent Workers’ Union of Great Britain, were dismissed in what the union argues constitutes unlawful and retaliatory dismissals.

“Organisers at the IWGB have reported that amongst the staff dismissed were those with visas sponsored by Rockstar and those with medical conditions who will lose access to essential workplace healthcare schemes.

“The IWGB, which sees this as a brazen act of illegal union busting, says it will be mounting a full and robust defence of its members who it believes have been targeted unfairly for exercising their legal rights.”

Alex Marshall, IWGB president, said: “Rockstar has just carried out the most blatant and ruthless act of union busting in the history of the games industry. This flagrant contempt for the law and for the lives of the workers who bring in their billions is an insult to their fans and the global industry.

“Despite this calculated attack on workers organising for a collective voice and to improve their difficult working conditions, the Rockstar union remains undeterred.

“They will keep organising for respect and better conditions whilst continuing to pour their blood, sweat and creativity into games that are loved by millions.

“The IWGB will pursue every legal claim possible to ensure our members are reinstated and receive interim relief.”

Spring McParlin-Jones, chair of the IWGB Game Workers Union, said: “Next year, Grand Theft Auto VI is expected to make upwards of 10 billion dollars (£7.6 billion).

“That’s enough to end world hunger for a year. Such a flagrant attack on workers’ rights from such a valuable studio sends a very clear and shocking message to the world, that money matters more than people.”

Alan Lewis, head of global corporate communications at Take Two Interactive, said: “We strive to make the world’s best entertainment properties by giving our best-in-class creative teams positive work environments and ongoing career opportunities.

“Our culture is focused on teamwork, excellence, and kindness. Rockstar Games terminated a small number of individuals for gross misconduct, and for no other reason. As always, we fully support Rockstar’s ambitions and approach.”