can corporations engage in speech that isn't commercial speech?

A Washington Post editorial entitled Free Speech for Nike is about the distinction between advertising of services and products, and a statement by a corporation regarding its business practices. Is it possible for a corporation to engage in free speech, and have those rights protected under the constitution? The article is also about a lawsuit in which the California Supreme Court

held that statements by Nike in response to criticism of its overseas business practices were commercial speech that, if false, could subject the company to liability under state law.

Is all speech from a corporation "commercial" speech? Can it ever be political speech, protected under the constitution? The editorial goes on to say that:

Under the California court's standard, many of the letters this page receives every day would be grist for lawsuits -- not against The Post, but against the companies whose representatives sent the letters.

I think that it is sometimes possible to distinquish between commercial and political speech made by a corporation based upon the forum and content. But, sometimes the differences between the two can be blurry at best, and that may argue against free speech rights for corporations. Here are some opinions and documents involving the Kasky v. Nike case:

Kasky v. Nike, Superior Court Opinion, via Corpwatch (April 20, 1998)
Kasky v. Nike opinion, Court of Appeal of the State of California, First Appellate District, Division One; via the California First Amendment Coalition (March 20, 2000)
ACLU Amicus Curiae brief (pdf), ACLU (December 20, 2000)
Greenwashing on Trial, Mother Jones (February 23, 2001)
Kasky v. Nike opinion (pdf), California Supreme Court (May 2, 2002)
PR Campaigns Lose Speech Protection, law.com (May 3, 2002)
Let Nike Stay in the Game New York Times (reg req'd) (May 6, 2002)
Court Rules that Nike Can’t "Just Do It", Center for Individual Freedom (May 10, 2002)
Modification of Supreme Court Opinion (pdf), California Supreme Court (May 22, 2002)
The ACLU's Position in Kasky v. Nike, ACLU of Northern California (May 31, 2002)
Nike, Inc. to Ask U.S. Supreme Court to Reaffirm First Amendment Right Of Businesses to Discuss Public Issues, News.com (August 1, 2002)