Up to ten tents belonging to International Protection applicants were slashed at a makeshift camp on the Grand Canal in Dublin.
Volunteers who support the men said their sleeping bags were also stolen on Wednesday, adding that they are growing increasingly concerned about the men's safety.
One volunteer said there had been around 17 men sleeping in tents on the banks of the Grand Canal the previous evening, and the camp had been tidied away the following morning.
Some of those who had been rough sleeping on Tuesday evening were offered accommodation on Wednesday, but the volunteer said a group of around eight or nine homeless IP applicants returned to the site that evening to their tents slashed and their sleeping bags stolen.
She said some of the men told the volunteers that "some guys came around threatening that they had to leave" earlier in the day.
She said the IP applicants had to sleep there again as there was nowhere else for them to go.
However, she said they did not get much sleep, "because they were pretty anxious about the whole thing".
She said there have been incidents of threats and intimidation before.
The volunteer added that there are anti-immigration groups who have been "setting up these patrols, and they're basically looking to try and find where the guys are camping" and posting these videos on social media.
Chief Executive of the Irish Refugee Council Nick Henderson said the charity is "deeply concerned about the situation of people seeking protection who are sleeping rough".
"In recent weeks, there has been a tangible increase in risk: tents have been slashed, camping spaces fenced off, and social media posts have circulated showing tents being filmed, accompanied by inflammatory commentary and threatening symbols such as flames," Mr Henderson said.
"In effect, the system requires people to sleep rough in order to demonstrate eligibility for accommodation, exposing them to serious harm. It also places enormous pressure on volunteers, who have supported people almost continuously for over two years," Mr Henderson added.
He stressed that figures released in response to a parliamentary question show that 1,400 people were refused accommodation upon arrival in the first four months of this year.
"While some may have been accommodated later, the fact remains: sleeping rough is never safe. We again call on the government to fulfil its legal obligations and support those seeking protection," he said.
