See this FEC press release about this conciliation agreement released today (after an earlier 5-1 vote, with then Commissioner Smith dissenting, and a new vote on the agreement, with Commissioners Weintraub and Lenhard dissenting). See also this report from the General Counsel, which formed the basis for the conciliation agreement. (I think I have the procedure and votes right here; if I’m wrong, I’d appreciate someone sending me an email with a correction.) Thanks to Brett Kappel for bringing this to my attention.
This resolution will be very important when it comes to voter guides, and I expect this issue will end up in court.
The press release begins:

The Sierra Club will pay a $28,000 civil penalty to settle charges that it used funds from its corporate treasury to pay for a brochure expressly advocating the election and defeat of candidates in the 2004 presidential and U.S. Senate races, the Federal Election Commission announced today.
“This is one of the most important express advocacy cases the Commission has resolved in recent years,” said Commission Chairman Michael Toner. “I am very pleased that the Commission was able to conciliate this case and provide further guidance to the public on the appropriate scope of the express advocacy test,” added Toner.
The settlement follows a Commission determination that the bar on using corporate treasury funds to pay for independent expenditures applies not only to communications containing so-called “magic words.” such as “vote for” or “vote against,” but also to a broader set of communications that are “unmistakable, unambiguous, and suggestive of only one meaning,” and can “only be interpreted by a reasonable person as containing advocacy of the defeat of one or more candidates.” This settlement with the Sierra Club, a 501(c)(4) organization, represents the first major case to consider the reach of the express advocacy test in light of the landmark Supreme Court case, McConnell v. FEC.
At issue was a pamphlet distributed by the Sierra Club in Florida prior to the 2004 general election. The front of the pamphlet exhorted the reader to “LET YOUR CONSCIENCE BE YOUR GUIDE,” accompanied by various nature scenes. The heading of the interior of the pamphlet urged the reader, “AND LET YOUR VOTE BE YOUR VOICE.”

The test used by the FEC appears at first glance to mirror the “backup” test for express advocacy in BCRA. The Supreme Court in McConnell did not have to reach the constitutionality of this backup test, having upheld the primary definition, containing a bright line test. Among other things, watch for an attack on this test as unconstitutionally vague.