In March last year, hundreds of journalists took the streets in Croatia. But they weren’t covering a news story, they were creating one: staging a rally to protest against the more than 1,000 lawsuits that have been brought against journalists in the country.

The Croatian Journalists’ Association, which organised the march, identified an astonishing 1,100 cases against news outlets and reporters filed by politicians and other public figures. But Croatia is far from being alone. Across the European Union, powerful and wealthy individuals and big business are tangling journalists up in legal knots to stifle public interest reporting.

Often starting with a letter from a law firm that forbids the journalist or media organisation in question from even disclosing the receipt of the letter, news organisations are told to halt publication, correct or withdraw stories – or face the possibility of a long, drawn-out legal battle, as experienced by The Shift.

Index on Censorship itself, which publishes a quarterly magazine on censorship, has been in receipt of such letters. They are written in terse, formal language that can make even the hardiest of reporters doubt themselves – even when they know with absolute certainty their story is true. We have heard from other news outlets that some letters request news outlets not just to delete or correct a story or face legal action – but tell a reporter they can never report on a particular individual again.

The Shift knows the format well, having been on the receiving end of countless such letters. Though The Shift reports such threats, others do not or cannot.

Robert Mihaljevic, editor in chief of Croatian regional newspaper Podravski, told news outlet DW last year that political strongmen were trying to silence “every critical voice” – using the threat of legal action as their weapon of choice.

“That’s why you can feel the need to self-censor in our newsroom,” he said. “I don’t even write my column anymore, because if I write it the way I want, lawsuits and compensation claims would endanger our jobs.”

This is the dark heart of the problem of such legal threats. Faced with the choice of dropping an important public interest story or heading into a legal battle that could bankrupt the organisation or the individual, and would suck up huge amounts of time (one Italian editor has estimated he spends three months out of every 12 fighting libel actions), news outlets often make the difficult decision to quietly pull a story or investigation.

A number of Maltese media organisations, for example, who were in receipt of the same threat of legal action as those received by murdered journalist Daphne Caruana Galizia, admitted they had pulled stories. And this is repeated across the region. One editor at a senior European newspaper – an organisation that has the good fortune to have its own legal counsel and funds for expensive court cases – told Index on Censorship that even their newspaper needs to “pick its battles”.

Fighting such threats can be exhausting, and isolating. Caruana Galizia was facing more than 40 suits at the time of her death, a pattern repeated in other countries where individual journalists might be fending off several law suits at a time. That’s a tough burden for a well-resourced news outlet, it is an impossible burden one for a freelance reporter.

Index on Censorship has heard anecdotally that insurance companies in some countries are now refusing to insure media organisations because of the rising number of so-called SLAPP law suits – those deliberately intended to frustrate public interest reporting through vexatious legal claims.

This has to stop. A free and independent media is the lifeblood of democracy. We need reporters to have the time and resources to investigate corruption and abuse of power in our societies. If they are tied up in lengthy, expensive legal cases brought by the powerful they cannot perform this crucial function.

That is why Index on Censorship has launched a new research project that aims to understand the extent of the problem. We know that one of the major problems is that journalists and media houses often feel unable to talk about these threats. Cases are settled and stories quietly dropped so that the media house can go on reporting.

We want to end that culture of silence. Our project will seek to gain as much information as possible about the law firms issuing legal threats, the laws being used to justify such actions – increasingly this involves the use of data protection and privacy laws rather than the traditional claim of defamation – and the actions taken by journalists and journalism organisations as a result.

Over the next few months we will be interviewing as many people as possible to get to the bottom of this problem and propose solutions, working with all those already doing fantastic work to combat such threats – including the likes of Greenpeace, Committee to Protect Journalists, European Centre for Press and Media Freedom, Reporters Without Borders and Scottish PEN.

Anyone who has ever received a letter from a lawyer over a story they know to have been accurate should get in touch and together we can push back against those who abuse the law to silence the media.