My interest is not in one particular case, but in a type of case (e.g., class action employment discrimination under Title VII of the 1964 Civil Rights Act, as amended). Is there a way to search for such cases on Pacer.gov?
You can search by Nature of Suit code at the individual court search websites, but not at the central search interface. That'll get you close, but it's not a title or section of code like you're hoping. Also, cases only get filed with one nature of suit code, so if it touches on multiple areas of the law, this can be a pretty terrible way to go.
The other approach you can look into, if you're looking for bulk data is to check out the Integrated Database provided by the Federal Judicial Center. It provides a CSV about all civil cases for the past decade or so that you can dig into. Check out the title, section, and subsection fields. The only issue here is that they're largely blank. My organization has a cheat sheet for the IDB if that's helpful.
Finally, if you want to be really thorough, the trick is to cast a really wide net, and to them filter the results somehow. So, for example, you could download the docket and initial complaint for all cases in a particular Nature of Suit code, and then search within those initial complaints for the particular law you're looking for. This tends to get very expensive fast, but it's a service we offer at my organization.
I think that's pretty much it for options. It's really not great, but the IDB is an underrated and mostly unknown resource.