AMSTERDAM, (Reuters) - The Netherlands moved to ban the sale of potent hashish cannabis on Thursday, eroding 40 years of liberal drug policy, over fears that the proceeds were flowing to organised crime gangs.

A parliamentary proposal to prohibit the sale of hashish resin in the Netherlands' famous coffee shops had the backing of both parties in the Liberal-Christian Democrat coalition. The sale of marijuana, the dried bud and leaves of the cannabis plant, will not be affected.

"Almost all of the hash that is sold in Dutch coffee shops is smuggled into the Netherlands by international criminal gangs from countries like Afghanistan, Morocco and Lebanon," said Ard van der Steur, a member of the ruling Liberal Party.

The ban on 'hash', derived from the potent TCH crystals on marijuana buds, will likely be in force by the end of 2013 and possibly sooner if changes to the law are swiftly implemented, he said.

The Netherlands is one of the few countries in the world where marijuana and hash are sold openly, but moves to crackdown on its sale have risen under the conservative government of Prime Minister Mark Rutte.

Another of those backing a ban, Christian Democrat legislator Coskun Coruz, said he hoped the ban would reduce consumption.

Studies show marijuana use in the Netherlands is roughly half that of the United States, where it is illegal.

Hash smokers in Amsterdam doubted a ban would cut use of the drug and said it would be hard to enforce.

"I know enough people to buy hash from if it is banned from coffee shops. I'm sure I'm not going to smoke less," 19-year-old Tommie van den Wouden said as he waited in line to order hash at one coffee shop in Amsterdam.

Ulrich, who works at a coffee shop, said about 40 percent of revenue came from hash sales but coffee shops would not be the only losers.

"If I can't sell hash any more, my customers will buy it on the street. This will also lead to declining tax income for the state," he said.

"I am surprised about these politicians saying they want to ban hash because of links with organised crime, because exactly the same goes for marijuana. The only difference is that most hash comes from abroad, while marijuana is grown locally."

As part of the crackdown, the Netherlands has introduced compulsory membership cards for coffee shops in the south of the country to deter drug tourists from Belgium, France and Germany. The rules came into effect in January but will not be enforced until May.

The government hopes to implement the measure nationwide, a move which would effectively herald the end of the Netherlands' position as a pot smokers' paradise.

While the sale of marijuana and hash is tolerated in the Netherlands, cultivating commercial supplies is illegal, making it complicated for coffee shop owners to acquire stock. 

Source: HuffingtonPost.com - Reporting by Tjibbe Hoekstra, Editing by Anthony Deutsch and Ben Harding