Disrespecting China's national anthem could carry a prison sentence of up to three years under a new draft law amendment, which may also affect Hong Kong and Macau, state media reported Tuesday.
It was unclear if the maximum penalty would apply in the two semi-autonomous southern cities.
But any move to punish anthem insults could trigger a backlash in Hong Kong, which enjoys rights and freedoms not seen on the mainland under a "One country, two systems" formula.
Some football fans in the self-governing city have booed the Chinese anthem when it was played at matches, despite appeals for restraint.
China has been fine-tuning legislation on the proper way and place to sing its national anthem, recently tightening rules that already bar people from performing it at parties, weddings and funerals.
The country in September passed a National Anthem Law applying to mainland citizens, which specified a much lesser jail term of 15 days for disrespecting the song.
Under the new measures to make the offence a crime, "punishment ranges from removal of political rights and public surveillance to criminal detention and imprisonment of up to three years", said the state news agency Xinhua.
China's legislature was this week deliberating the criminal law amendment and mulling whether to apply the existing law in Hong Kong and Macau, it added, without explaining why the penalty could increase so significantly.
It is not clear if Beijing could impose three-year jail terms in Hong Kong and Macau, since the cities are normally free to prescribe their own criminal punishments.
"My guess is that the penalties would apply partially to Hong Kong and Macau, at least through the National Anthem Law. This would carry a 15-day jail sentence," said Jeremy Daum of Yale Law School's Paul Tsai China Center in Beijing.
"That Hong Kong and Macau likely wouldn't get the three-year sentence should not make it sound mild, for such a ridiculous type of offence that doesn't hurt anyone and is an expression of free speech," Daum told AFP.
The former British colony returned to Chinese rule in 1997 under a promise that rights and freedoms would be protected for 50 years.
"In recent years, incidents of disrespecting the national anthem had occurred in Hong Kong, challenging the bottom line of the principle of 'One country, two systems' and social morality and triggering rage among Chinese," Xinhua cited Zhang Rongshun as saying.
"It is urgent and important to apply the national anthem law in Hong Kong, in a bid to prevent and handle such offences," said Zhang, deputy director of the National People's Congress Standing Committee legislative affairs commission.
Hong Kong's chief executive Carrie Lam said "protecting the dignity of the national anthem is the obligation" of her government, adding that exact details of the local legislation would have to be considered.
China's laws can be extended to Hong Kong by adding them to the city's mini-constitution, the Basic Law, followed by local legislative procedures.
Pro-democracy legislator Tanya Chan told AFP she had "great concern about how the law can influence our freedom of speech in Hong Kong".
- 'Chipping away at human rights -
In October Hong Kong fans booed and turned their backs during the playing of the "March of the Volunteers" anthem at a football match against Malaysia, despite appeals by football authorities.
There were also similar incidents at previous matches.
In 2015 during the World Cup qualifier between the city and its mainland rivals, Hong Kong fans jeered the anthem. That match followed pro-democracy protests in late 2014, which gripped the city and underlined discontent with Beijing's rule.
Amnesty International China researcher William Nee told AFP the anthem move "would clearly be out of step with international law".
"Besides being incompatible with the right to freedom of expression to begin with, extending the law to Hong Kong and Macau is also especially worrying," he said.
"It could be the first step in chipping away at internationally recognised human rights, using mainland China's nearly limitless and vague concept of national security -- which is often used to suppress peaceful expression of ideas and shield the Communist Party from scrutiny."
An ideological push has intensified in China since President Xi Jinping took power in 2012. The leader has stressed a drive to infuse every aspect of Chinese education with "patriotic spirit".