In some of its strongest anti-Muslim language to date, Poland's ruling Law and Justice party suggested Thursday that it does not want Muslim migrants to attend a major annual rock festival in the country this summer.

The nationalist party used Twitter to speak out against the Woodstock festival, which will take place in August in western Poland, not far from the German border. It referred to a statement made earlier by organizer Jerzy Owsiak, who said the event was open to migrants living in Germany.

"Do you really want to have an event in Poland with the participation of Muslim immigrants?" Law and Justice wrote, asking those who agreed to share the message.

Rafal Pankowski, the head of Never Again, an anti-racism group that has been involved with the festival for two decades, said he was shocked at the language.

"It is a very crude form of Islamophobic propaganda," Pankowski said. "The number of Muslims in Poland is very small anyway, so scaring people by using a supposed Muslim threat is artificial in the first place, but it's also cynical and unpleasant."

Also Thursday, President Andrzej Duda said he supports holding a referendum asking Poles if they want to accept refugees — but not until 2019, when people could weigh in as they vote in general elections, and only if migration is still a "problem" then.

Ewa Ostaszewska-Zuk with the Helsinki Foundation for Human Rights in Warsaw said she sees no reason for a referendum because the number of people seeking asylum in Poland is already low and the vote would serve mainly to promote anti-migrant sentiment.

"Right now the government talks about migrants in only one way: They are a threat to the security, they are dangerous, they are terrorists; we will not take anyone because we are looking after the safely of Poles," Ostaszewska-Zuk said.