Hong Kong is fast-tracking a homegrown national security law, following the one Beijing imposed in 2020 after quashing huge and sometimes violent pro-democracy protests.
The government bill -- expected to be put to a legislature vote within days -- proposes a maximum jail term of 14 years for any person who knows that someone will commit treason but fails to report it to the police.
The diocese's response comes against fears that the law could force Catholic priests to divulge information they heard in Confession to authorities.
In the three-sentence statement published on its website Diocese of Hong Kong said that it recognizes that citizens "have an obligation to ensure national security".
It has expressed its views on the proposed law, it said but did not elaborate on it.
The proposed security law "will not alter the confidential nature of Confession," said the statement issued in the name of the diocesan communication office.
UK-based activist group Hong Kong Watch earlier said the proposed law "directly threatens religious freedom," and in particular the confidentiality of the confession as it would force priests to reveal what was said in the confessional.
The former British colony is a common law jurisdiction with a legal system distinct from mainland China.
Hong Kong authorities defended the proposed criminal offense -- which used to be called "misprision of treason" -- saying that it had long existed in the city and other common law countries.
Responding to a lawmaker's question last week, Secretary for Justice Paul Lam said it would be "very difficult to create exceptions" for people like clergy and social workers regarding the offense.
The government has said the measure "has nothing to do with freedom of religion."
Hong Kong officials conducted a month-long public consultation on the security law and the subsequent legislative vetting took less than a week.
Around 390,000 of Hong Kong's 7.5 million people are Catholic, according to the diocese, and notable Catholics include two former city leaders.