It is a much different story for Schalke though, as they sit bottom of the table, with an imminent return to the 2.Bundesliga looking likely.
Match preview
Undoubtedly the biggest surprise package of the season anywhere in Europe, Union Berlin enter the weekend just one point behind Bundesliga leaders Bayern Munich.
They have stayed in touch with Bayern thanks to a fantastic 2-1 win at RB Leipzig last weekend, a result which ended Die Roten Bullen's 18-match unbeaten run.
It is a fairytale that a fan-owned club can compete with the might of Bayern and Leipzig, who are bankrolled by Red Bull.
Urs Fischer's side have won all six domestic matches since returning from the winter break, and they will fancy their chances of making it seven, given the fact they beat Schalke 6-1 in the reverse fixture - their biggest ever top-flight win.
Their supporters are living the dream in Europe too, and they came away from Amsterdam with a very respectable 0-0 draw against Ajax in the Europa League on Thursday.
Schalke meanwhile, are enduring the complete opposition at the moment, sitting bottom of the league and barely able to score a goal.
For the first time in their Bundesliga history, they have recorded three consecutive 0-0 draws.
However, that has at least earned them three potentially valuable points and restored some confidence in their defence after they lost their first two games post-World Cup by an aggregate score of 9-1.
They do look doomed though given their very feeble attack, as 0-0 draws are not going to get them out of the predicament they find themselves in.
Schalke have scored just 14 goals all season, nine fewer than the next worst side, as well as winning only one of their last 15 matches.
They are also winless away from home this season, which does not bode well for this fixture, having picked up just three points in their nine games on the road.
Rooted to the bottom of the table, they are five points off the relegation playoff spot, and seven points from safety, and it is a huge ask to expect anything from them here.
Union Berlin Bundesliga form:
L
W
W
W
W
W
Union Berlin form (all competitions):
W
W
W
W
W
D
Schalke 04 Bundesliga form:
L
L
L
D
D
D
Team News
Hungarian international Andras Schafer is the only injury absentee for Union Berlin coming into this one.
Fischer went with a full strength side in Amsterdam on Thursday so there is not expected to be many changes here.
Aissa Laidouni and Josip Juranovic have quickly become regulars in the Union side after their respective January transfers.
Schalke have a long list of injuries heading into this encounter.
Manager Thomas Reis revealed that Danny Latza, Marcin Kaminski and Niklas Tauer are back in training, but none of them will be back in time for the trip to Berlin.
Moritz Jenz became a father this week and was given a day off, but returned to training the following day and should feature here.
Tim Skarke is a doubt after he went off at half time last weekend, while Sepp van den Berg and Sebastian Polter are both out.
Union Berlin possible starting lineup:
Ronnow; Doekhi, Knoche, Diogo Leite; Juranovic, Khedira, Laidouni, Haberer, Roussilon; Becker, Behrens
Schalke 04 possible starting lineup:
Fahrmann; Brunner, Yoshida, Jenz, Uronen; Kral, Krauss, Zalazar; Kozuki, Frey, Butler
We say: Union Berlin 2-0 Schalke 04
Anything but a win for Union Berlin against the side bottom of the table would be devastating to their title hopes, and they must ensure they do not have one eye on their second leg with Ajax coming up.