In a televised address earlier on Thursday, Nawrocki said he would not sign the law implementing the SAFE programme in Poland, arguing that the loans could undermine the country’s sovereignty and economic security.
Kosiniak-Kamysz called the veto "a bad and dangerous decision," saying political interests had prevailed over responsibility for the armed forces.
“This decision is not against the government; it is against the security of the Polish state,” he said in a video statement released after the president’s announcement.
Kosiniak-Kamysz said the veto could slow efforts to accelerate the modernisation and transformation of Poland’s military but would not stop them.
“We will simply use other existing legal possibilities, such as the Armed Forces Support Fund, to carry out and accelerate the process of building the strongest army by 2030,” he said.
Government officials had already been preparing alternative options in case Nawrocki blocked the legislation, including the possibility of adopting measures through a Cabinet resolution, state news agency PAP reported.
Officials say the presidential veto will not prevent Poland from accessing SAFE funds, although it could complicate financing for services such as the Border Guard, police and the State Protection Service (SOP).
The interior ministry said Nawrocki's veto could deprive the police, Border Guard and State Protection Service of more than PLN 7 billion (EUR 1.6 billion) in funds for investment.
Poland was expected to be the largest beneficiary of the SAFE programme, potentially receiving about EUR 43.7 billion in low-interest loans to finance defence projects, much of it intended for the country’s arms industry.
Prime Minister Donald Tusk said the government would respond to Nawrocki's veto at an extraordinary meeting on Friday morning.
Zbigniew Bogucki, head of the President’s Office, is also expected to take part in the meeting.