The Federal Election Commission quietly issued an advisory opinion last week allowing candidates to raise unlimited money for issue-advocacy groups working on ballot measures in elections in which those candidates are on the ballot.
The opinion, issued in response to a request from a Nevada-based abortion rights group, could significantly alter the landscape in the fall in terms of the capacity that candidates aligned with these groups have to help them raise money.
The decision applies to all federal candidates, but with a presidential election taking place in six months, the biggest attention will fall to that race. If Mr. Biden can solicit money for abortion-rights ballot measures, he can add to an already-existing fund-raising advantage that his team currently has over Mr. Trump.
The decision could affect turnout in battleground states like Nevada where razor-thin margins will determine the election. In Arizona, an abortion rights group said it had the number of signatures required to put a referendum on the ballot. Florida — a state that has voted reliably for Republicans in recent presidential races — has a similar measure on the ballot.
The advisory opinion means that both Mr. Biden and former President Donald J. Trump can raise money for outside groups pushing ballot measures. In the wake of the repeal of Roe v. Wade, the landmark 1973 U.S. Supreme Court decision, abortion ballot measures are expected to be a key focus for Democrats this fall.
“I think it’s quite significant,” said Adav Noti, of the nonpartisan Campaign Legal Center, calling it an enormous change from prohibitions put in place by the landmark McCain-Feingold campaign finance bill in 2002.
The opinion was issued on May 1, in response to a question from lawyers representing the group Nevadans for Reproductive Freedom, which hopes to put a referendum on the ballot in the fall. Several lawyers, including the veteran Democratic election-law lawyer Marc Elias, represent the group.
The opinion found that federal candidates and officeholders can fund-raise for the group’s entities without being limited by dollar amounts or sources.
In a recognition of how the parties might see the opinion, the National Republican Senatorial Committee took issue with a draft of the measure a day before it was formalized. The objections included that such coordination between a candidate and an outside group would translate to a get-out-the-vote effort for Democrats in the Nevada effort, but the N.R.S.C. concerns went unheeded.
Of the six commissioners on the F.E.C., three Republicans and one Democrat agreed on the opinion.
A spokesman for the Biden campaign and a spokesman for the Democratic National Committee declined to comment.
The R.N.C.’s chief counsel, Charlie Spies, was pushed from his role after just two months amid a retreat for the committee’s donors in Palm Beach, Fla. A spokeswoman for the Trump team did not immediately respond to a question about whether Mr. Spies’s departure was at all connected to the advisory opinion.
But Chris LaCivita, a top adviser to Mr. Trump who is now helping steer the R.N.C. as its chief of staff, described the development as an opening.
“We will engage in all opportunities available, including new ones to defeat the corruption and failure of the Democrat machine,” Mr. LaCivita said.
Mr. Noti said that the bloc of commissioners had rendered other opinions of significant impact recently, including the expansion of the capabilities of super PACs.
“The combined effect of these decisions is having a really significant and demonstrable effect on how campaigns are run, and it’s all for the worse,” he said.
