Poland s Prime Minister Mateusz Morawiecki waits for the start of a round table meeting at an EU summit in Brussels, Thursday, Dec. 15, 2022. AP
The 27 member states struck a complex agreement on Monday that gave the greenlight to both the aid and a minimum 15 percent global corporate tax rate.
The so-called "megadeal", which included a compromise with Hungary freeing up some frozen EU funds, had been expected to be formally approved on Wednesday evening.
But repeated deadlines to ratify the package slipped by after Warsaw raised objections to the tax push.
The delay meant the wrangling spilled over into an EU leaders summit in Brussels on Thursday, setting up what was expected be a fraught standoff.
Poland -- one of the most hawkish supporters of Ukraine inside the EU -- insisted it was not opposed to 2023 financial aid to Kyiv.
But Prime Minister Mateusz Morawiecki said it was "blackmail" for other countries to maintain the money for Ukraine could only be agreed if the corporate tax deal went through.
The dispute comes as Poland looks to persuade the EU it has made enough progress on reforms to justify starting to receive $35 billion in post-Covid recovery funds.
Poland had previously stalled the tax plan to clear an earlier hurdle in that process, but had appeared to drop its opposition months ago.
In a separate disagreement, Warsaw was also objecting to a new package of sanctions on Russia over the war in Ukraine as it argued other EU nations had tried to water it down too much.
Poland said attempts by coastal states including Belgium and the Netherlands to roll back restrictions on Russia selling fertilisers would weaken EU attempts to punish the Kremlin.