from the Harvard Law Review:

https://drive.google.com/file/d/0B6FbJzwtHocwTWJ3VTJHSUFRTEU/view?usp=sharing

The conclusion of this article is as follows:

V. CONCLUSION
As I have tried to explain above, granting full First Amendment
protection to occupational speech is the only position that is consistent
with binding Supreme Court precedent. It is also the only position
that is consistent, more broadly, with the general trend of the Supreme
Court’s First Amendment jurisprudence over the last 20 years, which
has removed political speech from a position of privilege and now recognizes that speech on a wide variety of topics is entitled to robust
constitutional protection. Whether that was, as Post and Shanor argue,
a “radical[] ” shift when it began in the 1990s, it is now merely
the long-established law.
To be sure, there are those who wish this shift had never occurred,
but even its most ardent critics recognize that it has occurred.
Thus, whatever merit the…