WARSAW (Reuters) - Poland belongs in the European Union but should be careful not to be “infected by social diseases” that dominate the bloc, ruling Law and Justice (PiS) party leader Jaroslaw Kaczynski said on Sunday.

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Speaking at a party convention ahead of local elections in October, Poland’s most influential decision-maker laid out the broad campaign priorities of the PiS.

He defended his party’s democratic record and accused critics of serving “powerful interests and making deals with the mighty of the world”, in an apparent jab at the close ties between the liberal opposition in Poland and Brussels.

“I had said we would face an uphill battle and that stones would be thrown,” Kaczynski said.

“We are being attacked internally and from the outside ... in ways that discount the reality and aim to demean ... Poland,” he said.

“It’s easy to serve the interests of the most powerful. If you want to serve the society, the nation, it’s much more difficult.”

While underlining the need for Poland to remain inside the bloc, his party says the EU is forcing member states to conform to standards that contravene Poland’s traditional family values.

On Sunday, Kaczynski said EU membership was “the shortest way for Poland to achieve parity when it comes to living standards” with its western allies.

“But that doesn’t mean we should repeat the mistakes of the West and become infected with social diseases that dominate there,” he added.

The 69-year-old member of parliament has masterminded the country’s turn toward euroskepticism, traditional social values and protectionist economic policy.

Under Kaczynski’s leadership, Poland has grown increasingly isolated within the European Union, with the PiS government accused by opponents of a tilt toward authoritarianism.

Despite the criticism, PiS remains largely popular in Poland, ahead of the local elections, a European Parliament vote in May and a general ballot due late in 2019.

A strong result in the local elections would give PiS a better foothold in regional government and more say in how public funds are spent ahead of next year’s general election.

Kaczynski has been largely absent from the public eye in recent months, following knee surgery in May that kept him in hospital for weeks, fuelling speculation of tensions within PiS over who could succeed him at the party’s helm.