The vast majority of civil servants can sign a written declaration and senior civil servants, including the permanent secretary and department heads, are required to take an oath, Nip said on a radio program.

Nip stressed that even with the oath and written declaration, civil servants' freedom of speech will be guaranteed, but as they have responsibilities and requirements, there must be some restrictions on their words and deeds.

He said that if the words and deeds of a civil servant violated his oath, even if the words and deeds were not necessarily illegal, they will have breached the Civil Service Code and will be disciplined.

The contents of the oath and declaration are not new, as the Basic Law and the Civil Service Code have set out the relevant clauses, said Nip.

Signing the declaration and taking an oath can make civil servants more law-abiding and loyal to the HKSAR, as it is a public recognition and commitment, Nip stressed.

When speaking to reporters at the Legislative Council on September 25, he said, "For serving civil servants, we are following the established mechanism and in the process of consulting the major civil service staff unions and also our colleagues."

Civil servants will be dismissed if they violate their oaths or breach the national security law.

"It is also consistent with the National Security Law, particularly Article Six. So we introduce this requirement, and hope that through this requirement there can be a manifestation of the civil service's responsibility to uphold the Basic Law and pledge allegiance to the HKSAR, and also enable colleagues to be more aware of this responsibility," Nip said on September 25.

Michael Ngan Mo-chau, a Hong Kong civil servant, was demoted in June after he co-organized an illegal protest last August, reports said.