The Dutch government will press ahead with trials of regulated marijuana production with the maximum 10 cities when the experiment starts in 2021, broadcaster NOS said on Wednesday.

Tilburg, Almere and Breda are all on the list, which is due to be published on Thursday, the broadcaster said.

The experiment is part of the current government’s coalition agreement and was the express wish of the Liberal democratic party D66. The lower house voted in favour earlier this year, but the senate has yet to have its say.

The experiment with regulated growing is supposed to remove the gray area between the sale of marijuana in council-licenced coffee shops and the illegal cultivation and supply.

However, there are so many problems with the proposals that the big cities, where most of the coffee shops are located, see no point in joining in.

One issue is with the four year trial period, which will not be extended, even if the experiment is successful. This means that coffee shop owners will be forced back into the illegal circuit after four years of selling ‘legal’ marijuana.

Another objection is the requirement that all coffee shops within a council area take part in the scheme. In Amsterdam, with 175 coffee shops, this would be impossible to control, mayor Femke Halsema said.

In addition, the coffee shops would not be allowed to sell any ‘foreign’ hashish, which currently accounts for up to 25% of sales. This would drive users into the illegal circuit, experts say.