Both teams will be aiming to bounce back after crashing out of the DFB-Pokal quarter-finals in midweek, as they look to chase down league leaders Bayern Munich.
Match preview
Indeed, Dortmund were thoroughly outplayed by their former manager Marco Rose's RB Leipzig side at the Red Bull Arena on Wednesday, as they generated only two shots across the course of their 2-0 defeat.
Timo Werner's 22nd-minute strike gave the hosts the lead, which they richly deserved after enjoying a dominant opening period. However, BVB somehow managed to cling on until the very end, with Gregor Kobel clearly keen to make up for his huge error in Der Klassiker last weekend by making nine saves.
However, Willi Orban's last-gasp effort finally sealed the holders' progression to the last four of Germany's domestic cup, with Dortmund's only hope of winning a trophy this season now resting on their hopes of ending an 11-year wait for the Bundesliga title.
That job has become much harder after their 4-2 defeat to Bayern at the Allianz Arena last Saturday, with Edin Terzic's side falling 4-0 down to their arch rivals inside the opening 50 minutes, after Kobel's disastrous 13th-minute own goal had set the tone for a familiar defensive collapse against their foes.
Two late goals from Emre Can and Donyell Malen at least saved a small element of face for the visitors, who can not afford any more slip-ups from here on in if they are to overtake Bayern at the summit, especially as a defeat to Union Berlin on Saturday would see them leapfrogged into second by their opponents.
After only winning one of eight games in all competitions between mid-February and mid-March, back-to-back home wins either side of the recent international break have moved Union Berlin firmly back into the title picture.
Urs Fischer's side, who missed out on Champions League qualification by a solitary point last season, trail Bayern by only four points after their comfortable 3-0 victory against rock-bottom Stuttgart last weekend.
After a relatively dour first half, the in-form Sheraldo Becker broke the deadlock only six minutes after the break, with Kevin Behrens doubling the hosts' lead before Genki Haraguchi's own goal against his former club ended the match as a contest.
Die Eisernen's hopes of winning a cup competition this season were ended at the hands of Eintracht Frankfurt on Tuesday, though, with Randal Kolo Muani's early brace providing Fischer's side with a mountain too high to scale at Deutsch Bank Park.
Despite their recent exits from the Europa League and DFB-Pokal, Union Berlin clearly remain on course for achieving their primary goal: securing Champions League football for the first time in the club's history, with RB Leipzig's surprising 3-0 defeat at home to Mainz 05 last weekend helping them open up a six-point gap inside the top four places.
Fischer and his players will not allow their dreams to end there, of course, especially if they can spring an upset on Dortmund at Westfalenstadion on Saturday and move above their opponents into second place in the table.
Borussia Dortmund Bundesliga form:
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Borussia Dortmund form (all competitions):
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Union Berlin Bundesliga form:
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Union Berlin form (all competitions):
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Team News
Dortmund will almost certainly welcome Jude Bellingham back to their starting XI this weekend after only utilising the England midfielder from the bench during their 2-0 defeat to Leipzig in the cup on Wednesday.
Salih Ozcan is most likely to make way for the 19-year-old, but Terzic may opt to make no other changes, especially with Karim Adeyemi's absence from the travelling squad suggesting that he is not ready to start after his recent muscle injury.
Nico Schlotterbeck, Mateu Morey and Julian Duranville are all definitely ruled out through injury, while Sebastien Haller and Thomas Meunier are major doubts due to knee and back issues respectively.
Union Berlin, meanwhile, will desperately hope to have Fredrik Ronnow back in goal after the 30-year-old missed out against Frankfurt in midweek due to a knock.
Jerome Roussillon should return in order to provide natural balance at left wing-back, while Aissa Laidouni could return to the engine room after both players were unused substitutes on Tuesday.
Andras Schafer is expected to miss out once more due to his long-term foot injury, while Paul Seguin is also unlikely to feature after being withdrawn in Frankfurt due to a muscular issue.
Borussia Dortmund possible starting lineup:
Kobel; Wolf, Sule, Hummels, Ryerson; Bellingham, Can, Guerreiro; Brandt, Malen, Reus
Union Berlin possible starting lineup:
Ronnow; Doekhi, Knoche, Leite; Juranovic, Laidouni, Khedira, Haberer, Roussillon; Becker, Behrens
We say: Borussia Dortmund 1-2 Union Berlin
Dortmund's season appears to be unravelling at precisely the wrong moment of the campaign, with Terzic's side looking extremely insecure in their recent defeats to Bayern and Leipzig.
Union Berlin, on the other hand, should head into this match with real confidence of causing an upset, with Fischer's side perfectly poised to sting their opponents in transition.