Remarkably, Borussia Dortmund are sandwiched between table-topping Bayern and third-placed Union, with only five points separating the top six teams in the division.
Match preview
Having won each of the previous 10 Bundesliga titles, Bayern Munich's domination of German football has left other clubs with very little hope of success in recent years, but the perennial champions have not had it all their own way this season.
Granted, Bayern find themselves in a familiar position after 21 games, with the other 17 teams sitting below them in the standings, but Julian Nagelsmann's side are by no means running away with the title.
Not only are Borussia Dortmund and Union Berlin on the same number of points as Bayern, but Freiburg, RB Leipzig and Eintracht Frankfurt are also within touching distance of the frontrunners, making for a thrilling title race.
Although the Bavarians have suffered just two league defeats all season - picking up 12 wins along the way - they have been held to seven draws, while only FC Koln have recorded more draws this term.
It is also worth noting that Bayern have taken nine points from a possible 18 since the winter break, registering three consecutive 1-1 draws before notching back-to-back wins, with a 3-2 defeat to Borussia Monchengladbach coming last time out.
Of course, Bayern Munich are still the most feared team in Germany, but there is a sense that the club's hegemony over the Bundesliga could end this year.
Given Bayern's total dominance over the past decade, it may seem crazy that a club with just three full seasons of top-flight experience could halt the Bavarians' title streak, but it is a very real possibility.
Union Berlin gained promotion to the Bundesliga in 2020 and went on to finish 11th in their debut campaign, before finishing seventh in 2020-21 and fifth last term, and they now stand a genuine chance of clinching the title.
Urs Fischer's men chalked up five straight wins directly after the winter break, defeating Hoffenheim, Werder Bremen, Hertha Berlin, Mainz 05 and RB Leipzig in the process.
Although Union were held to a frustrating goalless draw by bottom club Schalke 04 last weekend, they bounced straight back with a 3-1 victory over Dutch giants Ajax in the Europa League on Thursday, booking their place in the last 16.
There is no hiding the fact that Union have struggled for goals at times this season, but they have remained defensively sound throughout the campaign, achieving the Bundesliga's second-best defensive record as a result.
The surprise package from the capital held Bayern Munich to a 1-1 draw in the reverse fixture back in September, despite seeing just 25% possession on home soil, so they will fancy their chances of securing another positive result against the defending champions.
Bayern Munich Bundesliga form:
D
D
D
W
W
L
Bayern Munich form (all competitions):
D
W
W
W
W
L
Union Berlin Bundesliga form:
W
W
W
W
W
D
Union Berlin form (all competitions):
W
W
W
D
D
W
Team News
Bayern Munich centre-back Dayot Upamecano is suspended for Sunday's clash after picking up a straight red card inside eight minutes against Borussia Monchengladbach last weekend.
Matthijs de Ligt is expected to replace Upamecano in the starting XI, while Leroy Sane, Jamal Musiala and Joao Cancelo are all in contention to return to the side after coming off the bench in the previous league outing.
With first-choice goalkeeper Manuel Neuer out for the season due to a broken leg, Yann Sommer will continue to deputise between the sticks, while defender Lucas Hernandez is also likely to miss the remainder of the campaign with an ACL injury.
As for Union Berlin, they will be without Andras Schafer this weekend, as the Hungarian midfielder has missed the past few games through injury.
The visitors will also have to make do without backup goalkeeper Jakob Busk, who looks set to miss the trip to Bavaria due to illness, so Frederik Ronnow will aim to seal back-to-back clean sheets in the Bundesliga.
Having bagged eight goals and seven assists across all competitions this season, Sheraldo Becker should be restored to Union's starting XI after dropping to the bench last weekend.
Bayern Munich possible starting lineup:
Sommer; Cancelo, De Ligt, Pavard, Davies; Kimmich, Goretzka; Coman, Musiala, Sane; Choupo-Moting
Union Berlin possible starting lineup:
Ronnow; Jaeckel, Leite, Knoche; Juranovic, Haberer, Laidouni, Khedira, Trimmel; Siebatcheu, Becker
We say: Bayern Munich 2-2 Union Berlin
Given that Bayern Munich have struggled to turn draws into wins this season, we can see a resilient Union Berlin outfit leaving the Allianz Arena with a point on Sunday.