Legal groups in South Africa have expressed concern over threats directed at the judge who found Oscar Pistorius guilty of culpable homicide not murder.
Thokozile Masipa has faced criticism since ruling the athlete did not kill his girlfriend intentionally.
Some of the remarks may border on hate speech, defamation and contempt of court, three legal groups said.
Protection for Ms Masipa has been stepped up since the verdict, South Africa’s City Press newspaper reports.
Police officers from the Tactical Response Team have been stationed outside her home and have also been escorting her, the paper said.
Ms Masipa became a judge in 1998 – the second black woman in the country’s history to reach that position.
The Olympic athlete denied murdering Reeva Steenkamp after a row on Valentine’s Day last year, saying he shot her by mistake believing there was an intruder in the house.
The BBC’s Pumza Fihlani in Johannesburg says some legal experts were surprised by last Friday’s verdict, but there have been more personal criticisms of Judge Masipa on social media.
It is the personal nature of these attacks that are of concern to the three legal groups, Legal Resources Centre, Section27 and the Centre for Child Law.
“Whilst it is understandable that people may disagree with the verdict, there is a significant difference between criticising the judgment and criticising the judge,” their statement said.
“These comments allege that Judge Masipa is corrupt, and/or that her gender and/or race rendered her incompetent in appropriately applying the law to the evidence presented.”
The statement said that her decision in the high-profile case last week required a considered application of the law in relation to the evidence presented.
“Attacking and threatening Judge Masipa because she is black or because she is female is simply unacceptable and should not be tolerated in our current constitutional framework, where equality and non-discrimination are of paramount importance,” the groups said.
South Africa’s prosecuting authority said it was “disappointed” that Pistorius was not convicted of murder but said it would wait until after sentencing on 13 October to decide whether to appeal.
The verdict leaves the disgraced sprinter facing up to 15 years in jail, although the judge could suspend the sentence or only impose a fine.