Long-running tensions between Poland's ruling nationalists and the bloc's liberal majority have risen sharply since Poland's Constitutional Tribunal ruled on Oct. 7 that elements of EU law were incompatible with the country's charter.
In challenging a central tenet of EU integration the case risks precipitating a new fundamental crisis for the bloc - still grappling with the after-effects of Brexit - as well as Poland losing generous European handouts.
"Some European institutions assume the right to decide on matters that have not been assigned to them," Morawiecki said at the start of two days of talks among the bloc's 27 national leaders in Brussels.
"We will not act under the pressure of blackmail, we are ready for dialogue, we do not agree to the ever-expanding competences (of EU institutions), but we will of course talk about how to resolve the current disputes in dialogue."
His wealthier Western counterparts are particularly keen to prevent their governments' cash contributions to the EU benefiting socially conservative politicians who they see as undercutting human rights fixed in European laws.
"We in Ireland are very concerned," Prime Minister Micheal Martin said. "The primacy of EU law... is critical for the protection of citizens all across Europe."
French President Emmanuel Macron told Morawiecki to work with the executive Commission to find a solution to the dispute compatible with European principles.
Dutch premier Mark Rutte singled out Poland's judicial overhaul that put courts under more government control. "We have to be tough," Rutte said. "The independence of the Polish judiciary is the key issue we have to discuss. It is very difficult to see how a big new fund of money could be made available to Poland when this is not settled."
Morawiecki's Law and Justice (PiS) party has raised the stakes in years of increasingly bitter feuds with the EU over a range of democratic principles from the freedom of courts and media to the rights of women, migrants and LGBT people.
The Commission has for now barred Warsaw from tapping into 57 billion euros ($66 billion) of emergency funds to help its economy emerge from the COVID-19 pandemic.
The top EU court may also slap more fines on Poland, the largest ex-communist EU country of 38 million people. That is the same court, the Luxembourg-based European Court of Justice (ECJ), that Morawiecki has accused of mounting a power grab.
For the bloc, the latest twist in feuds with the eurosceptic PiS also comes at a sensitive time. The EU - without Britain - last year achieved a major leap towards closer integration in agreeing joint borrowing to raise 750 billion euros for post-pandemic economic recovery, overcoming stiff resistance from states such as the Netherlands.
Morawiecki has dismissed the idea of leaving the EU in a "Polexit".
Support for membership remains very high in Poland, which has benefited enormously from funding coming from the bloc it joined in 2004.
But Warsaw - backed by Hungarian Prime Minister Viktor Orban - wants to return powers to national capitals and has lashed out at what it says are excessive powers of the Commission.
"Poland is one of the best European countries. There is no need for any sanctions, it's ridiculous," Orban said.
While many have grown increasingly frustrated at failed attempts to convince Warsaw to change tack, German Chancellor Angela Merkel warned against isolating Poland.
"We have to find ways of coming back together," she said, adding that having multiple legal cases against Poland brought to the ECJ was not a solution.
Her sway, however, is weakened as the veteran of more than 100 summits during her 16 years in power visits Brussels for what may be her last gathering of EU leaders before she hands over to a new German chancellor.
(Reporting by Marine Strauss, Bart Meijer, John Chalmers, Gabriela Baczynska, Philip Blenkinsop, Jan Strupczewski, Michel Rose, Andreas Rinke, Sabine Siebold; writing by Gabriela Baczynska; Editing by Richard Pullin, Alex Richardson and Andrew Heavens)