Razor blades have been hidden behind anti-5G posters on telegraph poles, telecoms engineers are being warned.
OpenReach workers were told to take care after blades and needles were found behind protest signs.
It comes amid a rise in the number of attacks on engineers, fuelled by a conspiracy theory wrongly linking 5G and coronavirus.
There were 68 incidents of verbal and physical abuse since 1 April as opposed to 42 for all of 2019, OpenReach said.
The company, which runs the broadband network for a range of internet service providers, said 56 of the reported attacks were linked to opposition to 5G.
Claims the wireless technology helps spread the virus have been condemned by scientists.
Engineer Aaron Ashton-Jones was driving to help a vulnerable customer in Kent when a car pulled in front of his OpenReach-branded van and slammed on the brakes.
The driver got out of his car and began shouting “all sorts of horrible words”, Mr Ashton-Jones said.
“He said, ‘you are spreading 5G, you are killing communities, you are the one who is spreading this virus’.”
Kent Police said it was investigating a report a man was verbally abused in Sittingbourne on 29 April.
Catherine Colloms, corporate affairs director at OpenReach, said there had been an “escalation” of attacks in recent weeks.
Engineers working on fixed broadband lines had wrongly been accused of installing the 5G network and causing both cancers and coronavirus, she said.
“A lot of it is verbal, a lot of it is quite unpleasant and really distressing for our engineers who are out there trying to do their job and keep the UK connected,” she said.
“We have had some instances of physical abuse, either threatened abuse or people have attacked, for example, an engineer’s van when they are working alongside it.”
Other engineers have been coughed at by people claiming to have Covid-19, she said.
An OpenReach spokeswoman said: “We’ve received reports from other telecommunications companies that anti-5G posters have started to appear on street equipment – particularly in London.
“On closer inspection, the posters have had razor blades and needles stuck on the back. Fortunately none of our engineers have encountered these dangerous items, but we’ve given them guidance about what to do if they do find any.”