Down more than 44% since its initial public offering (IPO), Snap Inc. (SNAP) was dealt another blow Monday when S&P Dow Jones Indices said that companies with multiple share classes will no longer be eligible for inclusion in the S&P Composite 1500 and related indices, including the S&P 500. "Companies with multiple share class structures are no longer eligible for inclusion in the S&P Composite 1500 and its component indices," said S&P Dow Jones in a statement.

The announcement means that Snap, which has multiple share classes so that its founders can maintain tight control of voting rights, is unlikely to find its way into some of the world's largest exchange-traded funds (ETFs), including the SPDR S&P 500 ETF (SPY) and the iShares Core S&P 500 ETF (IVV). SPY and IVV are the only ETFs with over $100 billion in assets under management. SPY is the world's largest ETF with nearly $243 billion in assets under management, while IVV has almost $122 billion in assets. (See also: Top 3 ETFs to Track the S&P 500 for 2017.)

Further rankling Snap investors is that S&P said companies that are currently members of benchmarks such as the S&P 500 that have multiple share classes will be "grandfathered in" and that the most recent announcement does not pertain to those firms. The S&P 500 is currently home to more than 500 stocks thanks to multiple share classes for some member firms.

For example, IVV holds 506 stocks because companies such as Google parent Alphabet Inc. (GOOG, GOOGL) and Warren Buffett's Berkshire Hathaway Inc. (BRK-A, BRK-B​) have more than one share class. The S&P announcement also pertains to the S&P SmallCap 600 Index and the S&P MidCap 400 Index, which are among the most widely followed gauges of U.S. small-cap and mid-cap equities. (See also: Why Would a Company Have Multiple Share Classes, and What Are Super Voting Shares?)

"Companies with multiple share class structures tend to have corporate governance structures that treat different shareholder classes unequally with respect to voting rights and other governance issues," said the index provider. "Therefore, S&P DJI's U.S. Index Committee will no longer consider these company structure types as future replacement candidates for the S&P Composite 1500 and its component indices, including the S&P 500."

Just a handful of ETFs currently hold shares of Snap. The Global X Social Media ETF (SOCL) has a Snap position of just under 3%, while the First Trust US Equity Opportunities ETF (FPX) allocates nearly 1% of its weight to shares of the social media firm. If Snap could qualify for entrance to S&P indices, ETFs and fund managers that benchmark to those indices would likely purchase the stock, potentially boosting the share price, a scenario that is off the table unless Snap liberalizes voting rights for common shareholders. (See also: Why Snap Stock Looks a Lot Like Facebook Right Now.)