Hartlieb was recalled from Triple-A Indianapolis on Sunday, Jason Mackey of the Pittsburgh Post-Gazette reports.
The 27-year-old had a brief stint in the majors during late April but is still looking to make his season debut with the Pirates. Hartlieb posted a 3.63 ERA, 1.57 WHIP and 19:19 K:BB over 22.1 innings last season.