Unions, businesses and interest groups of all political stripes may run TV and radio "issue ads" that name candidates in the days before elections, federal regulators said Tuesday, easing previous restrictions and opening the way for groups to influence next year's elections with big-money advertising campaigns.

Following the lead of the Supreme Court, the Federal Election Commission voted unanimously to soften its advertising rules in a decision that could lead to fresh ads as soon as next month in Iowa.

Under the change, an organization that supports a presidential candidate, for example, may use corporate or union money to run independent ads that cast the candidate in a good light or that criticize his rivals, provided the overall message is a call to action on a public policy issue.

The FEC had little choice. The Supreme Court had ruled in June that restrictions on such ads were unconstitutional but offered no clear guidelines for what types of ads would be affected.

A 2002 campaign finance law, whose co-author was Republican presidential candidate John McCain, banned corporations and unions from paying for issue ads within two months of a general election and 30 days of a primary election.

Under the rules adopted Tuesday, issue ads that mention a political candidate will be permissible in the weeks before an election as long as they focus on a matter of public policy and don't mention an election, political party or an opposing candidate. But the FEC also left the door open for other ads if commissioners determine that their main focus is a public policy issue or a commercial transaction.

Commissioners voted 4-1 to require that financing for any advertising paid for by unions or corporations be publicly disclosed — a provision supported by several campaign finance watchdog groups.

Campaign finance lawyers have been watching the FEC, given that the blackout period for ads in Iowa is only 13 days away. Among the unions monitoring the case was the Iowa branch of the Service Employees International Union. That branch has endorsed Democrat John Edwards.

Corporate or labor backed groups will still be prohibited from running ads that specifically call for the election or defeat of a candidate. Only candidate committees and political action committees, whose donors can give only limited amounts of money, are allowed to air such "express advocacy" ads.

The Supreme Court decision was based on ads aired by Wisconsin Right to Life Inc., an organization that mentioned Democratic Sen. Russ Feingold, who was up for re-election in 2004, and which called on him and other senators to stop filibustering Bush judicial appointees. The group sued the FEC arguing that by not being able to run the ads during the pre-election blackout period the government had violated its rights.

Commissioners on Tuesday conceded that the new FEC regulation will invite further legal tests.

"One thing we know absolutely for certain is that we're going to go beyond WRTL," Commissioner David Mason said, referring to the initials for the court case.

Critics of the Supreme Court's ruling and the FEC's new regulations say groups will now be able to run thinly disguised issue ads that would have the same effect as outright campaign ads

Richard L. Hasen, a campaign finance expert at Loyola law School Los Angeles, offered examples in his Web log of the types of ads that would be permitted under the new regulation:

— "Call Sen. Clinton and tell her to stop coddling illegal aliens and terrorists by supporting the NY driver's license plan" (Clinton had seemed open to considering the plan for New York, but has since rejected the idea).

— "Call Mitt Romney and tell him more of our soldiers shouldn't die in an unnecessary war in Iraq."

The commissioners clearly struggled with the language of the regulation. They considered two draft proposals. One would have required corporations and unions to identify publicly the financing sources of any electioneering communication; the other would not have required financial disclosure.

The two proposals invited last minute suggestions from campaign finance lawyers, including the attorney who argued the Supreme Court case that led to the regulation. Commissioners initially had scheduled a vote on the regulation for their 10 a.m. meeting Tuesday, but postponed the session to the afternoon.

In the end, the provision they adopted was based on proposals by Commission Chairman Robert D. Lenhard and Commissioner Ellen Weintraub.

Hasen said it was prudent for the FEC to issue guidelines given the disagreements over the impact of the Supreme Court ruling.

"People may be tempted to blame the FEC; the FEC is a convenient whipping boy" he said. "But the opening is absolutely called for by the Supreme Court opinion."