More than a dozen people were injured in skirmishes in Kyiv as Ukrainians protested against controversial plans to allow the sale of farmland.
Ukraine was known as the "breadbasket of Europe" and has 32.5 million hectares of arable land, twice as much as France.
Currently, the farmland can only be rented but a new proposal would open up its sale to Ukrainians or foreigners.
On Tuesday, several thousand people — including farmers and nationalists — gathered outside the parliament building in the Ukrainian capital.
People threw stones and bricks at the police, who retaliated using tear gas. Two large tents set up by protesters were torn down by police, according to AFP journalists.
What is this draft law about?
It proposes to scrap a 2001 rule banning the sale of farmland.
The bill passed its first reading on November 13 but MPs must give it a second reading before October 2020.
Ukraine has 32.5 million hectares of arable land, which is among the most fertile in the world. Currently, these can only be rented and not sold.
According to the draft law, anyone — including foreign citizens and companies — who have been using Ukrainian land for at least three years (for example, by renting it), would be able to acquire ownership.
World Bank estimates this opening of the market could lead to an additional 1.5 points growth in Ukraine.
The country is among the poorest countries in Europe.
Why are protesters concerned?
According to polls, between half and two-thirds of Ukrainians are opposed to this draft law, fearing that it will only benefit Ukrainian oligarchs and foreigners.
"Foreigners are going to buy our land. I fear for my territory, for the future of our children," Alina Tcherkachyna, a young farm worker who came to demonstrate in Kyiv from central Ukraine, told AFP.
"It is the farmers living on these lands who must take possession of them and not the big landowners," says farmer Valeriï Ichtchenko, 56, from the Vinnytsia region (centre-west).
In a bid to reassure, Ukraine's president, Volodymyr Zelenskiy has promised a referendum before opening the market to foreigners.