Traditional marriage supporters are outraged over a California judge's decision to broadcast the Proposition 8 trial on YouTube.
San Francisco Federal Judge Vaughn Walker made the last-minute decision based on what he called an experimental basis.
The hearing involves two same-sex couples who argue the voter-backed, pro-traditional marriage legislation violates the U.S. Constitution.
Gay rights groups say the coverage will help expose the American public to the arguments and evidence by both sides and to the judicial process.
But opponents argue that it could jeopardize the safety of the witnesses involved.
"These proponents and supporters and donors have, in the past, been subject to harrassment, intimidation and even death threats," Brian Brown, executive director of the National Organization for Marriage, said.
"Taking a high profile case like this in which the constitutional rights of the Prop 8 supporters are being threatened and putting it on television, will undoubtedly increase threats and possible harm to witnesses and people involved in the case," he added.
The court usually bans television, radio and photography from the courtroom.
Walker is the first federal trial judge to exercise the experimental program.