The Bundesliga debutants are feeling the impact of not playing league games, which have been suspended by the German Football Association until at least early May.
Union Berlin look like securing their Bundesliga status for another season as they lie 11th on the league table, eight points clear of the relegation places with nine games remaining.
"These are exceptional circumstances we have to deal with," said Union president Dirk Zingler in a statement.
"Our club's purpose is football. If it ceases to exist, then it will touch the core of our existence.
"The management, our staff, the squad and backroom staff have worked hard in recent months to ensure success in the Bundesliga. Now they are giving up a lot of money to get through this crisis together.
"This willingness cannot be credited highly enough to everyone involved. On behalf of the club's entire management, I would like to thank them for their support.
"As a club, we'll conquer the challenges ahead and this will best happen, if we work together as the Union family."
The players of Borussia Monchengladbach have also agreed to waive their salaries in the current circumstances while Bayern Munich and Borussia Dortmund players have agreed to a reduction in their wages.
Germany have so far recorded 35,740 Covid-19 cases and 186 deaths.
