BRUSSELS (Reuters) - The European Union executive asked the bloc's top court on Monday to fine Poland for violating a ban on logging in an ancient forest, but Warsaw said it was only trying to preserve unique woods.

The row over the three-fold increase in timber production in the primeval Bialowieza forest is being closely followed by environmental groups but also feeds into a wider clash between the EU and its biggest eastern member.

Brussels accuses Poland's nationalist and eurosceptic ruling party, Law and Justice (PiS), of undermining democratic standards, including weakening judicial independence.

The Commission says Poland has ignored an order by the Luxembourg-based European Court of Justice (ECJ) in July to immediately stop logging in the forest, a UNESCO World Heritage site and home to the largest herd of European bison and unique birds and insects.

The halt was meant to prevent irreversible damage to the delicate ecosystem before a final ruling on whether the higher timber production in Bialowieza violates EU nature preservation laws, as the executive European Commission argues.

At Monday's hearing, a Commission lawyer showed satellite pictures to prove Warsaw was violating the injunction, and said the Commission would ask the court to fine Poland. It has four days to file a formal request including the size of daily fines it deems justified.

Poland's Environment Minister Jan Szyszko told the hearing the logging was only to save the forest from a major beetle outbreak and that it respected EU laws, taking place only in regular parts of the forest, not in the protected national park.

He said taking out infected trees was an important public security measure because the weakened ones could fall on people picking mushrooms or berries in the woods.

Environmental group ClientEarth said in a statement that argument did not hold, adding that the case is the first time in EU history that a country has disobeyed an ECJ decision.

The Commission has cited what it says is Warsaw's violation of the ECJ order to stop logging as part of broader concerns about the rule of law in the EU's largest ex-communist state.

Multiple feuds between the PiS government and Brussels have soured sentiment towards Poland, which joined the EU in 2004 and was seen for years as a poster child for the transition from totalitarianism to democracy.

(Reporting by Gabriela Baczynska; Editing by Catherine Evans)