Tens of thousands of people have taken to the streets of cities throughout India to protest an economic policy you probably haven’t heard of before: demonetization.

Three weeks ago, Indian Prime Minister Narendra Modi surprised his country with an announcement banning 500- and 1,000-rupee notes — worth about $7 and $15 respectively — in a bid to tackle corruption and terrorism.

He estimated that forcing people to exchange the country’s largest currency bills for new banknotes would allow the government to crack down on “black money” — unaccounted-for cash holdings that haven’t been taxed but, under the law, should be. He also argued that it would strike at domestic terrorist financing operations by capturing counterfeit money and rendering the legitimate cash they kept in the shadows worthless.

Banning widely used banknotes would have a huge impact on any economy, but in India the policy is transformative. Modi’s sudden ban instantly meant that 86 percent of all the cash in circulation in India was no longer considered legal tender, which means that businesses could refuse to accept those bills as a form of payment. And the Indian economy simply runs on cash: It’s estimated that between 90 and 98 percent of all transactions in India, measured in terms of volume, involve it.

Unsurprisingly, Modi’s demonetization initiative has caused chaos across the country. People want new banknotes, but the current supply of them isn’t close to meeting demand. That’s created headaches for people as they wait in long lines outside ATMs and banks, which routinely run out of cash. For people who rely on daily cash earnings to survive, it can mean not being able to obtain food.

The temporary shortage of banknotes is having other far-reaching effects. Farmers looking to sow their next set of crops can’t buy the full quantity of seeds they need. Property sales, which typically require huge cash investments, are slowing. It’s even reshaping cultural life: Weddings, which can cost millions of rupees, are taking a serious hit.

“A lot of marriages are being postponed, and those that are managing are doing so by borrowing from relatives and friends,” says Niranjan Sahoo, a senior fellow with the Observer Research Foundation, a think tank in New Delhi.

Modi’s agenda to crack down on black money makes sense in theory but it isn't working smoothly in practice. It's hitting individual Indians hard, and the country itself may pay a heavy price: Many economists expect the growth of India’s booming economy to slow substantially in the final quarter of 2016.

How does the ban work?

As of November 8, old 500- and 1,000-rupee notes are no longer legal tender. That means if you try to buy lunch with them, a restaurant owner can refuse to accept them.

People in India have until the end of the year to go to banks and replace those notes with other bills, including the new 500- and 2,000-rupee notes.

If someone wants to convert more than 250,000 rupees — roughly $3,650 — they’re required by law to provide an explanation for why they have so much cash and prove that they’ve paid tax on it. If they don’t, they’re expected to pay a fine of 200 percent of the tax they owe.

Why is this happening?

The primary reason Modi initiated the ban is to force people with illegal cash holdings to deposit the money into bank accounts and pay taxes on them.

India’s government collects a tiny fraction of the taxes that advanced democracies do. The government recently released data that showed that in 2013, merely 1 percent of Indians paid taxes. As Kaushik Basu, former chief economic adviser to the Indian government, recently noted at the New York Times, the most reliable estimate of India’s “shadow economy,” or the untaxed part of it, puts it at one-fifth of the country’s GDP.

The demonetization scheme is also a way to crack down on criminal activity. It will be hard for people with large cash holdings from purely criminal enterprises to explain how they paid their taxes, and so they won’t be able deposit their money. And the government expects to be able to use the ban as an opportunity to round up counterfeit currency minted by terrorist operations.

In addition to all this, the ban also serves as a natural prompt for India to transition to a cashless society, dovetailing nicely with Modi’s bid to digitize services in the economy.

What are the effects so far?

The currency ban has been a huge headache for millions of Indians. Since the old 500- and 1,000-rupee notes are the bread and butter of most financial transactions in India, everybody has been rushing to exchange them. But because the supply of new banknotes is far smaller than the supply of old ones, there are currently strict regulations on the quantity of new banknotes that people can withdraw at any given moment. And even with these regulations, reports of banks running out of cash abound.

“Every day — and today is the 20th day — you can see there are long queues for ATM machines and banks,” Sahoo says.

The cash shortage has been particularly hard on destitute Indians, many of whom don’t have bank accounts. Some of them have to choose between waiting in line for a day to exchange their defunct currency or working for a day’s wages. And Basu estimates that many poor people may simply end up losing their savings because of their mistrust of financial institutions and concern about being harassed about where their cash came from.

“The policy is poorly implemented and has a high cost for those who are least able to bear it,” Rohini Pande, an economist at Harvard’s Kennedy School, said. “Even if [the government is] able to reduce corruption somewhat, you have to balance that against costs or other ways of reducing black money.”

Many experts don’t even have faith that this is an effective way to counteract tax evasion. Basu says that most black money doesn’t take the form of cash held in india but is instead held in gold, silver, real estate, and overseas bank accounts.

Modi is using a very crude tool to crack down on black money. For many, the costs are likely to end up more tangible than the benefits.