Leverkusen, who won the domestic league and Cup double last season without a single defeat, crushed Heidenheim in the league 5-2 last week before firing another five goals past RB Salzburg in the Champions League on Tuesday in a 5-0 win.
Yet they have managed three consecutive victories across all competitions only once this season, back in September.
"We want to have again a good feeling. After (the win over) Heidenheim it was better and it was certainly better after Salzburg," coach Xabi Alonso told a press conference ahead of Saturday's match.
"Tomorrow is a different game... but it is a good moment to show that after two good games, we can play a third good one in a row. I want another clean sheet tomorrow."
Leverkusen have managed just one win in their last four league games and are fourth on 20 points, nine off leaders Bayern Munich who face Borussia Dortmund on Saturday.
"We know we expect something different against Union and a big challenge in front of us," Alonso said.
"We have to be prepared for a physical game."