WASHINGTON - American viewers will now have online access to information identifying which groups are buying campaign commercials, under a new Federal Communications Commission rule.

Starting Tuesday, all television stations are required to report and publish online details about the political ads they air.

"You're flying blind as a voter," said Kathy Kiely, managing editor of the Sunlight Foundation, a nonpartisan, nonprofit organizations that advocates for open government.

Get Breaking News Delivered to Your Inbox

"You need to know who is influencing your vote, and unless you know who they are, you can't determine that," Kiely said.

Nonprofit organizations are not required to register with the Federal Election Commission, as long as their commercials meet certain criteria. "It can't say who to vote for or who not to vote for and it can't air within 30 days of the primary or 60 days of the elections," said Kiely.

This lack of transparency allowed some groups to fly under the radar while pushing an agenda. According to the Sunlight Foundation, nonprofit groups spent at least $300 million in the 2012 campaign.

The new mandate allows the public to readily identify which groups are buying campaign commercials and how much they are spending.

It is an expansion of the 2012 ruling that required top 50 market affiliates of ABC, CBS, FOX and NBC to post their political ad details online. Now, more than 2,000 stations will be required to do the same.

The Sunlight Foundation filed a complaint earlier with the FCC asking for greater enforcement of the 2012 mandate.

"This represents a rare victory for transparency in a political system increasingly inundated with dark money," the group said Tuesday.

Dark money is a term used to describe money that is donated to a campaign from an undisclosed source.

In an election year where there are competitive Senate races in states such as Alaska, Iowa and Arkansas, where there is no station in a top 50 market, the public now has more access to see who is trying to influence their vote.

Spanish-language stations Univision and Telemundo, which reach an important demographic for upcoming elections, are also covered by the rule.

Access to a group's campaign ad spending is just a few clicks away. Through the FCC website, each station's data can be searched through "public inspection files."

Additionally, the Sunlight Foundation created Political Ad Sleuth, a site where ad spending information can be searched using a committee's name or the ad name.