NEW YORK —In a possible escalation of a campaign against a separatist movement, the Hong Kong government appears ready to take steps to bar a third opposition politician from the semiautonomous Chinese city’s legislature.

The Justice Department said the city government would issue proceedings against the legislator, Lau Siu-lai, who was sworn into office this month. The Justice Department declined to be specific, but prodemocracy politicians said it was most likely because Lau had read her oath of office very slowly, in an apparent act of protest.

The move against Lau, a teacher who participated in 2014 protests for freer local elections but who has not called for separation from China — as had the two legislators who were denied their seats on the Legislative Council — has raised concerns about a broader crackdown on opposition politicians, beyond separatists.

Nathan Law, a prominent student leader in the 2014 protests who, at 23, is the youngest-ever member of the legislature, said the government has “declared war’’ against all pro-democracy parties.

“The government is trying to take us down one by one,’’ he said. “It’s full-blown authoritarian suppression.’’

The High Court barred the two pro-independence politicians from office after they altered the words of the oath during their swearing-in last month, pledging allegiance to the “Hong Kong nation.’’

Lau, in contrast, had read the oath word for word; she did so extremely slowly. The legislature first accepted then rejected her oath in October, but she was sworn in this month after she agreed to reread it normally.

New York Times