The Mets will call Hartlieb up from Triple-A Syracuse to have him serve as the 27th man for Wednesday's twin bill with the Nationals, Tim Britton of The Athletic reports.
The Mets and Nationals won't be playing a traditional doubleheader; the first game will be a resumption of Tuesday's contest, which was suspended in the second inning with Washington leading, 3-1. Regardless, Hartlieb's status as the 27th man means he'll likely be sent back to Syracuse after the two games are completed. Through six big-league appearances between the Mets and Pirates this season, Hartlieb has given up eight earned runs on seven hits and nine walks across seven innings.