A UN report into the humanitarian impact of Israel's West Bank barrier says it has caused widespread losses to Palestinian farmers.
Closed gates often prevent the farmers from getting onto their land
About 5,000 Palestinians currently live in the areas between the barrier and Israel's pre-1967 boundary and they need permits to get in and out.
The UN says farmers are not being allowed access to farmland, causing unemployment and loss of income.
Israel says the barrier is justified to counter bomb attacks by Palestinians.
About half of the 700km-long barrier's system of electric fences and high concrete walls has been built so far.
The focus of the latest UN report is access to farmland in the closed areas.
UN official Allegra Pacheco says the barrier is having a worrying economic impact on people who live close to it.
"Our biggest concern is that farmers are increasingly not being allowed access to their farmland located west of the barrier.
"Either through the very complicated permit system that requires proof of land ownership - and that's at this point quite difficult - and also because of the operation of the gates."
Ms Pacheco says many of the gates provided by the Israeli army to allow the passage of farm workers are either kept closed or only open for limited times.
The UN is worried that if the land is not cultivated it may eventually be confiscated.
An Israeli spokesman said any problems the barrier might cause Palestinians were not comparable to the benefits it brought in terms of Israeli lives it is saving.
The UN says its report would not have been necessary if the barrier had been built along the Green Line, the boundary between Israel and the West Bank before the 1967 war.
Nearly 75% of the barrier lies on territory occupied by Israel in 1967.