Some barristers and lawmakers warned yesterday's judgment could mean new immigrants were also eligible for other rights usually reserved for permanent residents.
Non-permanent residents in Hong Kong - immigrants who have not yet lived in the city for seven years - are only entitled to some publicly funded benefits, such as health care and subsidised transport.
"[Yesterday's ruling] has far-reaching effects," warned Nelson Chow Wing-sun, professor of social work at the University of Hong Kong. "Even the government may not be able to tell exactly how many policies and how many people are affected."
Barrister and Civic Party lawmaker Alan Leong Kah-kit urged the government to conduct a comprehensive review of who is now eligible for public subsidy schemes.
"The government should find out how the judgment affects public policy and come up with solutions," Leong said.
He voiced concern that the city's public housing would now have to be opened up to new immigrants.
In contrast, Professor Albert Chen Hung-yee, dean of HKU's Faculty of Law, believed the judgment related only to Comprehensive Social Security Assistance (CSSA), and said it did not merit seeking a reinterpretation of the Basic Law by the National People's Congress Standing Committee.
HKU principal law lecturer Eric Cheung Tat-ming, said the judgment favoured the government, as it made clear that the court would only interfere in its decisions if a policy was "manifestly without reasonable foundation".
The judgment indicated that while the government may not be able to do whatever it wanted, "the bar is still very low", Cheung said. He added: "The court has to keep the proper balance."
Cheung agreed it was only the CSSA policy that was ruled unconstitutional and did not believe the case affected other social welfare policies.
Secretary for Labour and Welfare Matthew Cheung Kin-chung said the department would be assessing the effect of the judgment.
Currently, all residents receive public health care services at local prices, and all elderly people aged 70 or above are offered HK$1,000 coupons under the Elderly Health Care Voucher Scheme, regardless of their residency status.
A transport subsidy provided by the Labour Department is also offered to all legally employed residents.
The right to participate in politics is restricted to permanent residents, as is the Old Age Living Allowance and a disability allowance.
Non-permanent residents are also barred from applying for government jobs, including the uniformed services.