The decision comes amid a wave of threats to the two MKs who had been teetering between voting in support of or against the new coalition led by Yamina head Naftali Bennett and Yesh Atid head Yair Lapid.
Yamina MK Ayelet Shaked has also been assigned a security detail and since last week, the Shin Bet has provided Bennett with a full prime-ministerial-level security detail.
Silman announced that she would be supporting the "change bloc" in forming a coalition with center- and left-wing parties. Orbach has yet to formally announce his decision.
As a result, right-wing protesters have been demonstrating outside Orbach's home, calling on him to leave his camp and vow to oppose the new coalition.
Yair Netanyahu, Prime Minister Benjamin Netanyahu's son, had his Twitter account temporarily suspended on Friday after he posted Orbach's home address to help guide protesters to it.