Eastern Europe is warning David Cameron against meddling with “sacrosanct” migrant worker rights, as the newly re-elected prime minister prepares to renegotiate Britain’s EU membership terms.

While Mr Cameron’s election victory has been greeted positively from across Europe, Britain’s traditional allies in the east are already preparing for a fight to defend the free movement rights of migrant workers.

“They cannot be touched,” Peter Javorčík, Slovakia’s Europe minister, told the Financial Times.

Szabolcs Takács, Hungary’s EU minister, called freedom of movement a “red line”, adding that it was one of the EU’s biggest achievements. “We don’t like it when Hungarian workers are called migrants, they are EU citizens with the freedom to work in other European countries,” he said.

Meanwhile Rafał Trzaskowski, Poland’s Europe minister, said: “We are ready to sit at the table and talk about what needs to be reformed . . . but when it comes to immigration, our red lines are well known.”

Britain has in the past counted former communist countries in central and eastern Europe as natural allies, but Mr Cameron has hurt relations in recent years by his tough stance on migration.

José Manuel Barroso, former European Commission president, said on Monday the principle of free movement of people was inviolable but that Mr Cameron “had a point” in wanting to stop “some abuses of our social security systems” by migrant workers.

Mr Barroso said if Mr Cameron approached his renegotiation in a positive spirit it was possible to have “a good conversation” with other EU leaders. “The tone is very important,” he said.

He also told the BBC’s Today programme that the prime minister had “renewed legitimacy and greater internal authority” after this election victory and that Ukip had become “almost irrelevant” in the British debate.

“He is someone who is determined and pragmatic,” Mr Barroso said.

The Europe issue is set to become the biggest flashpoint in Mr Cameron’s pursuit of a “new deal” for Britain, which he will put to an in-out referendum on UK membership of the bloc by 2017.

His election victory last week was accompanied by signs from leaders in western Europe that they would try to help him reset Britain’s relationship with the EU.

Angela Merkel, German chancellor, described his win as “simply great” and François Hollande, French president, called Mr Cameron on the day of his victory to invite him to Paris. Jean-Claude Juncker, European Commission president, said: “I stand ready to work with you to strike a fair deal for the United Kingdom in the EU.”