One candidate takes money from an international activist group that doesn’t disclose the names of the overwhelming majority of its donors. The other takes money from Virginia’s biggest utility, which is also the top lobbyist in the state.

As Lt. Gov. Ralph Northam and former congressman Tom Perriello battle for the Democratic nomination for governor, their fundraising is emerging as an issue that defines them as much as their slim differences on policy.

Northam has called on Perriello to renounce “dark money,” just days after Perriello disclosed $230,000 in contributions from an international activist group called Avaaz, which Perriello helped found a decade ago.

[Perriello’s governor’s bid boosted by several big donors]

As a 501(c)(4) charity, Avaaz is not required to disclose its individual donors, which it says come from among nearly 45 million members in 194 countries.

Virginia Lt. Gov. Ralph Northam (D), who is running for governor. (Matt McClain/The Washington Post)

The organization says it accepts no money from governments or corporations and itemizes any donations greater than $5,000 on its tax filing; in 2016, 26 such donations were reported, representing 0.7 percent of Avaaz’s total revenue.

Perriello co-founded Avaaz with two colleagues who had helped him start an earlier nonprofit called Res Publica, which was aimed at promoting international justice on behalf of the religious left, as Perriello told the National Catholic Reporter in 2004. One of those colleagues, Ricken Patel, a Canadian, is now Avaaz’s executive director. The organization was formed in collaboration with MoveOn.org, the Democratic online activist group that has received funding from billionaire George Soros — who also is a major Perriello campaign contributor.

Avaaz says it sets priorities for its lobbying campaigns and protest events through online membership polls. Among the top causes in 2016 were protecting sea life, supporting the Paris climate agreement and breaking the grip of big agribusiness companies such as Monsanto.

Although the organization spent some $400,000 to oppose President Trump’s election campaign last year, according to OpenSecrets.org, its website doesn’t reflect much participation in elections. The donation to Perriello’s campaign was the first of its kind, Avaaz spokesman Will Davies said: “The first time Avaaz has ever donated to a political campaign in the U.S.”

Because the organization is not required to disclose individual donors, it is hard to tell whether the Avaaz money came from foreign sources, which would violate federal election law.

Emma Ruby-Sachs, the deputy director of New York-based Avaaz, said the big Perriello donation “is actually hundreds of small online donations from hundreds of Americans who are members of Avaaz that were transferred in one lump sum.”

The organization has a system to ensure the money is coming from U.S. donors, similar to methods used by other online fundraising groups such as ActBlue, Ruby-Sachs said.

Ruby-Sachs said 71 percent of Avaaz members in the United States voted in an online poll to support Perriello’s campaign.

The Perriello campaign listed a $200,000 Avaaz donation on Jan. 5, the same day the former congressman stunned Virginia’s political establishment by announcing that he would compete against Northam for the nomination.

That raised questions about how Avaaz could have polled its members in time. But the organization and campaign said Friday that the listed date was incorrect and that the Avaaz money arrived on Jan. 19 and Jan. 27 . A Perriello spokesman said the campaign would correct the filing.

The seed money from Avaaz was among several large donations included last week in Perriello’s first campaign finance disclosure, which showed that he outraised Northam in the first three months of the year but has less cash on hand.

Northam was prohibited by state law from fundraising for the 46 days the General Assembly was in session.

Perriello’s biggest donation was $500,000 in kickoff money from Sonjia Smith, a Democratic contributor from his home town of Charlottesville.

Overall, however, Perriello drew far more from out-of-state sources than Northam — 57 percent for Perriello compared with 11 percent for Northam — according to the nonpartisan Virginia Public Access Project (VPAP).

Northam has been quick to emphasize the differences in the two candidates’ donor bases. After Smith published an essay in the Roanoke Times titled “I contributed $500,000 to Tom Perriello. Here’s why,” the Northam campaign jabbed back with a piece titled “I contributed $50 to Ralph Northam — here’s why,” highlighting seven of his grass-roots donors.

Perriello’s campaign declined to comment specifically on the Avaaz contributions. Instead, a spokesman highlighted money that Northam has received from the state’s biggest utility — Dominion Power — and from the health insurer Anthem.

“Tom’s largest contributions came from people long familiar with his advocacy work on progressive causes, not from individuals or corporations with business interests before the state like Dominion or Anthem,” Perriello spokesman Ian Sams said. “So when it comes to money influencing politics, we’ll let Virginians decide which of these sources of contributions are more troubling.”

Northam reported $5,000 from Dominion chief executive Thomas F. Farrell II in the first quarter of this year and took more than $20,000 from the corporation in 2016, according to VPAP.

This comes at a time when Dominion’s huge influence in Richmond is under scrutiny. More than 60 Democratic candidates in upcoming House of Delegates races have signed a pledge refusing to take money from Dominion, and Perriello has rejected the utility’s money as well.

Northam’s campaign emphasized that 92 percent of his contributions were $100 or less and said he is not influenced by big money.

“The only influence on Ralph Northam’s vote is what’s in the best interest of Virginians,” campaign spokesman David Turner said.

An earlier version of this story incorrectly reported the dates that Avaaz made two donations to the Perriello campaign. This story has been updated.