Workers on Victoria's north-south water pipeline say they have been threatened with iron bars and had speeding cars swerve at them.
The workers, who say they are alarmed about a string of incidents over the past two months, have complained to police as anger about the pipe simmers in country Victoria.
The Australian Workers Union will meet pipeline workers on Friday, with the union saying work crews might need protection.
So far, at least four reported incidents have led to police inquiries.
Two workers had an iron bar waved at them while on a lunch break in October.
The workers say they were called "rats" and "dogs" by an angry man who later produced an iron bar and asked, "How would you like some of this?"
Police also investigated an incident the next day when workers said a car travelling close to 120 km/h swerved within a metre of them.
In late September, another complaint was lodged when a speeding car travelled within 30 centimetres of a worker with its horn blaring.
Police are still investigating an incident two weeks ago in which a worker was clipped by a car after a pipeline protest near Glenburn at which eight people were arrested.
Construction companies involved in the project became so concerned about their workers being targeted that they set up a phone hotline on which local businesses could declare they were happy to accept trade from pipeline workers.
AWU state secretary Cesar Melhem said he would wait until after Friday's meeting before deciding whether extra protection was needed.
"We are monitoring the situation closely, but let me tell you I will not stand by and watch people put our members at risk," he said.
"If we get to a stage where we feel our members' safety is being put at risk, we will be asking the Government to take some extreme measures to make sure our members are protected on that job, and if that includes having security and police presence then that's what has got to happen."
Anti-pipe campaigners are planning a non-violent protest at the construction site near Glenburn today.
Some anti-pipeline campaigners have urged protesters not to target workers.
Moments before the protest that led to eight arrests earlier this month, The Age witnessed protest leader Jan Beer tell protesters not to touch workers or equipment.
She told the group that their "beef" was with the Government, not the workers.
Ms Beer said she was confident her campaigners would act in the right spirit, but said workers were straying onto roads, creating an unsafe situation for themselves and motorists.
"I would hope no one is going to do something (violent) … We've not heard of anything, but I can see how angry people might be."
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