Stalls have had to keep their shutters down in Norwich Market after traders found their premises surrounded by barriers.
Some of the pavement has been dug up along Gentleman's Walk with barriers in place directly in front of four stalls on the Gaol Hill side of the market.
Two of these stalls closed on Tuesday as a result of the works.
Ray Harvey, of the Harvey's Cards stall, said: "Staff just turned up this morning to see chaos left at the front.
"The Jubilee weekend is coming up and we are expecting it to be a bit busier so this is not the best timing.
"The stalls at the front can't work today as there is nowhere for people to get to them. They are in an impossible situation."
Some traders believe the work is to do with broadband connection in the area.
Ali Lakshmanasamy, who works at Orient Express in the market, said: "We did not know what was happening when we first saw it this morning.
"Trade has been a bit slow today but I hope it's OK and picks up a bit. I feel bad for the pet store at the front as they have been cut off.
"It's a bit annoying but we are still here."
Joe Silvester, who oversees Joe's Pets in the market, praised workers for minimising disruption by pledging to work overnight.
But he added: "It has affected customer levels because the stalls are blocked off.
"The work has encroached on market land which I do not think they know about.
"The council have been brilliant about it and ensured there is swift action to get issues sorted. This is nothing to do with them."
Another trader, who did not wish to be named, said: "It's ridiculous and a couple of stalls have just decided to shut today.
"It's just a shame to do it when the kids are off during half-term."
It is understood the works are being carried out by Virgin Media and are expected to last from 7pm on Monday to midnight on Wednesday.
The barriers will be reduced in the coming days.
Virgin Media has been contacted for comment.
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