Philadelphia area soda distributors and grocers are reporting a 50 percent drop in sugar-sweetened beverage sales so far this year.

That's after the Philly City Council voted last summer to implement a 1.5 cent-per-ounce soda tax, aimed at curbing sales of unhealthy drinks while generating revenue for city infrastructure and education projects.

And so far, it's working - though mostly in low-income neighborhoods, where residents are most likely to feel the effects of the tax. The price of a 12-pack of cans has doubled.

Technically, the levy is assessed at the distributor level, so it's not a tax and it's up to them whether or not to pass the tax on to their customers.

"In 30 years of business, there's never been a circumstance in which we've ever had a sales decline of any significant amount," said Jeff Brown, chief executive officer of Brown's Super Stores, to Bloomberg. "I would describe the impact as nothing less than devastating."

Canada Dry Delaware Valley Chief Operating Officer Bob Brockway, who distributes more than 20 percent of all soft drinks in the Philadelphia market, also told Bloomberg he expects his business will decline by at least a third over the course of the year, and layoffs are likely.

But advocates of the tax say it's doing exactly what it should.

"This is just an attempt by industry to whip up the troops and try to turn back sound public policy," Jim Krieger, executive director of Healthy Food America, said to Bloomberg. "The bottom line is that the purpose of the tax was to raise money for important needs and to serve the residents of Philadelphia, and it's doing precisely that."

Philadelphia was the second U.S. city to implement a soda tax, after Berkeley, Calif. in 2014.

After Philly passed the soda tax, a number of cities followed suit, including San Francisco; Oakland; Boulder, Colo.; and Cook County, Illinois. Mexico also has a hugely successful soda tax, and new research says soda sales there keep falling.

Experts say it's too early to tell the long term effects of the tax in Philadelphia, but it's likely consumers will start buying soda again once they're used to the new prices.

The tax is expected to generate $409.5 million over five year, $314 million of which would go to programs such as expanding pre-kindergarten and renovating recreation centers and libraries.

Read More:

• Philadelphia's Soda Sellers Say Tax Has Reduced Sales by as Much as 50% (Bloomberg)
• Philly Soda Tax: Third Time's A Charm? (Earth Eats)
• Sales Fall Again in Mexico's Second Year of Taxing Soda (New York Times)