HONG KONG (Reuters) - A year ago, growing anti-government demonstrations in Hong Kong were a hot topic in conversations among bankers, lawyers and other investment professionals in one of the world’s biggest and freest financial hubs.

On Thursday, two days after China imposed a controversial new security law on the city, you could almost hear a pin drop. Bankers were tight lipped, shunning any mention of the legislation over the phone or messaging apps in a sign of how much disquiet it has triggered.

More than half a dozen people Reuters spoke to said they chose not to talk about the impact of the law on their businesses with their colleagues and external contacts, though there had been no such official instruction from their respective organizations.

The sweeping legislation pushed the semi-autonomous city, which is the regional home for a large number of global financial companies, on to a more authoritarian path.

The law punishes crimes of secession, subversion, terrorism and collusion with foreign forces with up to life in prison.

While it doesn’t directly impact the financial sector, its provisions including giving a special police unit extra powers of search, electronic surveillance and asset seizure that have stoked concerns among some professionals.

‘IT COULD CHANGE THE WAY WE COMMUNICATE’ Both Hong Kong and Chinese government officials have said the law is vital to plug gaping holes in national security defences exposed by months of sometimes violent protests against the local government and Beijing over the last year.

But critics fear it will crush freedoms and an independent legal system that are seen as key to Hong Kong’s success as a financial centre and a gateway between China and the world.

“I was on a call with Singapore colleagues this morning when one of them asked me about the law and its impact on Hong Kong,” said an executive at a regional insurance company, who like his peers declined to be identified citing the sensitivity of the matter.

“I had just started when my boss tapped me on the shoulder and asked me to move on to business matters. Later, all our team members in Hong Kong were told to strictly refrain from sharing opinion on this on calls and social media.”

While most financial professionals in Hong Kong have long been aware of being tracked by the world’s most sophisticated electronic surveillance system when they travel to China, they said they have had no such concerns or need for precautions in Hong Kong.

A corporate lawyer with an international law firm said that could change the way in which people in the former British colony “communicate and correspond” from now on.

“I think some people could become very careful in what they write on Whatsapp and Wechat ... as a firm we are not writing anything in any correspondence like that (related to the law) but it could become an issue for some.”

Some of the professionals said that they were also reviewing their previous posts on social media related to the pro-democracy protests and the security law, and deleting ones they thought would be viewed as sensitive.

A senior Hong Kong-based wealth manager with an European bank said that he had been advised by his manager to minimize his conversations over messaging apps with his local clients about any political impact on markets and investments.

One financial analyst who was arranging a meeting in a café said it might need to be held somewhere more private if the conversation included the new security law.

“Walls have ears now,” he said.