The CDU chairman Friedrich Merz has threatened not to approve the planned special fund of 100 billion euros for the Bundeswehr.
The Union will not allow finished results to be presented, "which we should then simply agree to," said Merz of the "Bild am Sonntag".
"If the chancellor wants to persuade us to change the Basic Law and for 100 billion euros in new debt, then he has to talk to us."
Merz demanded from Chancellor Olaf Scholz (SPD) that the 100 billion euros “only benefit the rearmament of the Bundeswehr”.
In addition, at least two percent of gross domestic product must be spent on defense in the long term.
"If these requirements are met and a repayment plan is also submitted for the new debts, then we can agree," said Merz.
As the "Bild am Sonntag" reported, a proposal from the Chancellery is currently causing trouble: The Bundeswehr special fund could be submitted to Parliament for a vote without an attached economic plan.
The Union sees itself restricted in its right to have a say in individual armaments projects, as the newspaper reported.
Criticism of such an approach also comes from the ranks of the governing parties.
"Smoke Candles" and "Half Truth"
In the debate about arms deliveries to Ukraine, Merz sharply criticized Chancellor Scholz.
He throws "one smoke candle after the other".
Merz told the "Bild am Sonntag".
"He covers up, he doesn't tell, he only tells half the truth".
Germany is therefore increasingly isolated internationally.
Merz warned of an escalation of the war if Ukraine did not receive sufficient military support: "It is precisely the refusal to use heavy weapons that makes the escalation and expansion of this war more and more likely," said the CDU leader.
"The last few years have shown: (Russia's President Vladimir) Putin will always go on if he is not stopped."