Occupations are strongly sorted by ideology. Political scientist Adam Bonica has produced reliable and consistent estimates of ideological placement for a huge number of individuals, politicians, and organizations. As he writes here, he was especially struck by how extreme are the mean ideology scores for various occupations:
Although the ideological orientation of these industries is not much of a surprise, the extent to which these industries favor the extreme, rather than moderate, wings of each party far surpassed my expectations. Some of the distributions more closely resemble what I would expect from occupations that were subject to the spoils system–for instance, US postmasters prior to the Pendleton Act–than major contemporary industries with no official partisan ties.
In Bonica's AJPS article, he makes a similar observation:
In some industries, ideological sorting easily exceeds the levels of sorting observed along geographic or economic lines.
An interesting wrinkle in this data is that the left-leaning occupations are more left-leaning than the right-leaning occupations are right-leaning. Of the left-wing occupations and organizations, there are many firmly below -1, but for the right-wing occupations there are very few above 1. Indeed, even iconic representatives of evil right-wing military-industrial capital — such as Boeing or Exxon Mobil — are essentially centrist, at least with respect to their staffing.
You can see this again when he places industries into three buckets: Left, Right, and Divided. In the graphs below, it's easy to eyeball that the peak of the left-wing distributions are further to the left than the peak of the right-wing distributions are to the right.
What are the underlying variables that explain how occupations sort into these three baskets? Just speculating, the left-wing occupations seem to be mostly about social performance and they garner high status. The right-wing occupations are mostly about mundane things and garner zero or negative status. And the divided occupations are those that call for ambiguous combinations of these things (person-facing but socially unimpressive).
And because some of those graphs are a bit old (2008), here is some confirmation that the basic patterns have not changed, at least as late as 2012.