The Iron Ones find themselves five points shy of Borussia Dortmund and seven points behind Bayern Munich, while Gladbach occupy 10th place in the table.
Match preview
Borussia Monchengladbach recorded a hard-fought 1-1 draw at Eintracht Frankfurt last time out, as Randal Kolo Muani's 83rd-minute strike saw the hosts come from behind to snatch a point after Jonas Hofmann's early opener.
Thanks to that draw, the Foals head into Sunday's clash on a four-game unbeaten run, having registered one win and three draws since their last loss.
Gladbach maintained their impressive home form with a 2-0 victory over Wolfsburg a fortnight ago, meaning that Daniel Farke's men have avoided defeat in each of their last five Bundesliga matches at Borussia-Park.
Better still, Borussia MG have lost just one of their previous eight home league games, picking up four wins and three draws along the way, with February's 3-2 victory over Bayern Munich still fresh in the memory.
There is no hiding the fact that Gladbach have experienced a wildly inconsistent campaign up to now, recording nine wins, nine draws and 10 losses in the league, but recent results point towards a strong end to the season.
It could be argued that Union Berlin's unlikely title bid is already over, with perennial champions Bayern Munich sitting seven points clear of the plucky challengers, but the Iron Ones will continue to fight until the very end.
The fact that Union are even involved in the title race with six games remaining is remarkable in itself, given that Urs Fischer's side gained promotion to the Bundesliga for the very first time in 2019.
Union Berlin made an outstanding start to the current campaign, winning 13 of their opening 20 Bundesliga matches, but they have fallen off the pace in recent weeks, winning just two of their previous eight league outings.
Following a four-game winless run across February and March, Union secured wins over Eintracht Frankfurt and Stuttgart before losing to Borussia Dortmund, with a 1-1 draw against relegation strugglers VfL Bochum coming last weekend.
Although Fischer's men have struggled for consistency of late - taking 10 points from a possible 24 since a five-match winning streak earlier this year - Union have proved that they have what it takes to finish the season on a high note.
Borussia Monchengladbach Bundesliga form:
D
L
D
D
W
D
Union Berlin Bundesliga form:
D
D
W
W
L
D
Union Berlin form (all competitions):
L
W
W
L
L
D
Team News
Borussia Monchengladbach look set to be without the injured trio of Yvandro Borges Sanches, Nico Elvedi and Tony Jantschke this weekend.
With Alassane Plea also expected to miss Sunday's clash due to illness, Lars Stindl should come into the starting XI to join Florian Neuhaus and Jonas Hofmann in support of striker Marcus Thuram.
Marvin Friedrich is likely to replace the injured Elvedi at centre-back, joining Ko Itakura at the heart of Gladbach's defence.
As for Union Berlin, Paul Jaeckel is suspended after receiving a red card in last weekend's draw with Bochum, so Diogo Leite is expected to come into the visitors' backline.
The Iron Ones also remain without long-term absentee Andras Schafer, who last featured for the first team back in January before picking up a foot injury.
Rani Khedira will continue to anchor the midfield, with Sheraldo Becker and Kevin Behrens resuming their partnership in attack.
Borussia Monchengladbach possible starting lineup:
Omlin; Scally, Itakura, Friedrich, Bensebaini; Weigl, Kone; Hoffman, Neuhaus, Stindl; Thuram
Union Berlin possible starting lineup:
Ronnow; Leite, Knoche, Doekhi; Juranovic, Laidouni, Khedira, Haberer, Roussillon; Becker, Behrens
We say: Borussia Monchengladbach 1-1 Union Berlin
Union Berlin will be desperate to remain within touching distance of the top two, but the visitors look set to drop more points this weekend as Borussia Monchengladbach extend their unbeaten run on home soil to six matches.