"I will have to dismiss at least half of my 16 employees" when the ban on cultivating and selling the so-called magic mushrooms enters into force on December 1, Schaap told AFP on his farm in Tiel in the central Netherlands.
McSmart, the business he created in 2000, produces some 25 tonnes a year of the substance known fondly by users as "shrooms" and in the Netherlands as "paddos".
"The ban makes no sense," protests the 36-year-old entrepreneur, saying he felt angry and deceived.
Declining to detail his turnover, Schaap deplores the "hundreds of thousands of euros" he had invested in the fresh mushroom industry, which unlike the already banned dried variety has thus far been traded freely in the Netherlands.
"I've been set back ten years. I've lost everything," said Schaap.
In vast sheds among lush, green agricultural fields, McSmart cultivates different types of hallucinogenic mushrooms from the spore phase right through to their packaging in 30-gramme plastic punnets.
After being cultivated in laboratories, the mushrooms are grown to adulthood in the half-dark on a bed of compost, straw and fertilizer.
They grow so fast that sometimes McSmart staff have to harvest more than once a day, after which the fungi are immediately packaged for consumption and shipped off to specialized Dutch vending points known as "smart shops" where a punnet containing two doses is sold for about 12 euros.
According to industry association VLOS, there are six growers in the Netherlands, 180 smart shops and a few hundred employees in an industry with an annual turnover of 15-20 million euros.
Announcing the ban this week, health minister Ab Klink said the consumption of paddos "can lead to unpredictable and risky behavior".
Authorities drew up a list of 186 species of mushrooms whose sale will be banned in future. More are expected to follow later.
This may have been easier to accept, said Schaap, "had there been a good reason for the ban, like for cigarettes that takes the lives of thousands of people every year".
He claimed that mushrooms have never been proved to be harmful, and proclaims pride in the product of which he was a keen consumer when younger.
"The use of mushrooms gives you insight, it should be part of growing up. It is a nice experience, friendly. People experience it positively - it is something you should do two or three times in your life."
He blames the ban on posturing by political parties, adding: "It will simply pave the way for illegal trade without any control or guarantee of quality".
According to Amsterdam health authorities, more than 90 percent of the 1.5- to 2 million doses of mushrooms consumed annually are sold to foreign tourists.
A quarter of smart shops are found in the Dutch capital.
The death in March last year of a French teenager who had taken mushrooms before jumping to her death from an Amsterdam bridge, reignited the debate over the hallucinogenic fungus.
Though no link had been established between the product and the girl's death, it led a majority of MPs to call for a ban.
VLOS has announced that it would seek compensation for its members, like Schaap, from Dutch courts.
"We will try to stay afloat a few months longer by producing those hallucinogenic mushrooms which are not yet on the government list, but that will not save my business," said Schaap.
There has been a heated national debate in recent weeks about the Netherlands' famously liberal drugs laws, as more and more MPs seek a reconsideration of the tolerant approach to so-called soft drugs like marijuana.
There have also been calls for the closure of the famous Dutch coffee shops where marijuana is sold.