A 23-year-old clerk will be the first adult allowed to testify in court via a live television link because she is too frightened to give evidence in an open court.
Ma Jing will testify against her former boss, finance company manager Wong Kwai-nam, in the District Court on Friday.
The Crown alleges Wong, 30, who denies intimidation and sending threatening mail to prominent people, instructed Ms Ma to write some of the letters.
The prosecution team said the witness was too afraid to testify in open court. John McLanachan, defending, opposed the application.
In accordance with a directive laid down by Chief Justice Sir Ti Liang Yang, their arguments on the issue were heard in chambers by trial Judge Pang Kin-kee.
Since February this year, vulnerable witnesses - including alleged sex abuse victims, alleged crime victims under the age of 14 and mentally handicapped people - have the option of testifying via closed-circuit television.