Hartlieb was recalled by the Mets on Saturday, Justin Toscano of The Bergen Record reports.
Hartlieb was up as the extra man for Wednesday's doubleheader but did not get into either game. He was sent back to Triple-A Syracuse following the game but is back with the team just three days later and will try to improve on his 10.29 ERA and 2.29 WHIP, numbers he's recorded in seven innings of relief.