"This is about nothing less than maintaining Germany's ability to act on its security policy," André Wüstner, head of the Bundeswehrverband (army union) said on Thursday.
Wüstner says that the army needs at least €18.5 billion over the coming four years, almost double what the cabinet agreed on Wednesday.
"The under-financing of the Bundeswehr [German army] is far from ended" by Wednesday's move from Chancellor Angela Merkel and her team, although it's a step in the right direction, he said.
Defence Minister Ursula von der Leyen, of Merkel's Christian Democratic Union (CDU) has said that she wants to spend €130 billion on Germany's military over the coming 15 years to finally modernize the force and end its long-running equipment problems.
German Defence Minister Ursula von der Leyen posing with mountain troops during a training exercise in Bad Reichenhall, Bavaria, on Wednesday. Photo: DPA
But even with the budget increase announced on Wednesday, Germany will remain far removed from the Nato target of spending two percent of Gross Domestic Product (GDP) on defence.
In fact, the Federal Republic will remain stuck at around 1.2 percent of GDP spent on its armed forces.
Years of underspending by Germany have earned it criticism from its foreign allies, especially the US and UK, which spend a much higher share of their budgets on defence than large European countries like Germany, France, or Italy.
The Social Democratic Party (SPD), currently governing in coalition with the CDU, joined in the army union criticism of the budget plans.
Adding just €10 billion to the budget was "completely insufficient," Rainer Arnold, senior SPD MP on the German parliament defence committee, told Die Welt on Thursday.
SEE ALSO: History of the German army