The SEC has passed a new rule that will likely make mutual fund companies greener - in more ways than one.

The Securities and Exchange Commission it will no longer require mutual fund companies to mail biannual reports to shareholders who haven't opted for e-delivery. Under the measure, called Rule 30e-3, fund companies will save $2 billion in the next decade, and will decide for themselves whether to pass the savings on to consumers, according to the Investment Company Institute.

"These actions are an important part of the Commission's effort to better serve Main Street investors in our ever changing marketplace," SEC Chairman Jay Clayton said in a statement. "The new rule significantly modernizes delivery options for fund information while preserving the right of fund investors to receive information in paper form as they do today."

Beginning in 2021, investors will receive a notice in the regular mail that their report has been published online, instead of the report itself, which typically runs a few dozen pages. Less tech savvy investors will be able to opt to request paper copies, but they will no longer be the default.

About half of investors have already chosen to get their reports e-delivered, Executive Director of the Coalition for Paper Options John Runyan estimates, but shifting to online statements may disadvantage elderly and low income investors, many of whom invest in mutual funds through their 401(k)s.

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"Forty percent of the elderly don't have internet access and then throw in the investors who are reluctant to do business online. Are we just supposed to forget those people?" Runyan said. "It's the SEC's job to care more about investors than the people running the firms."

Initially proposed in 2015, the SEC announced it would consider changing its policy on shareholder reports on Friday, when it released the agenda for Tuesday's open meeting. However, the rule was voted on behind closed doors Monday and the outcome announced in a press release Tuesday morning.

"This was a missed opportunity for the SEC to step back from the mutual fund industry's clamor for cost reduction and think about what investors really need," Runyan said. "Investors won't see a dime of the savings."

The decision is a "cost-saving win" for mutual funds, Capital Alpha Partners analyst Ian Katz wrote in a report Sunday. Fidelity Investments alone mails 21 million shareholder reports annually, according to Senior Director of External Communications Meghan Reilly.

"We see this as a real win for investors," Reilly said. "It will bring the investment community into the 21st century and empower savers to view the information they need in an interactive way."