Activists for gender and sexuality rights in Poland say they expect a record turnout at an “equality parade” in Warsaw on Saturday, amid a climate of growing hostility towards minorities and claims that the government is curbing human rights.

A number of diplomats will be in the crowd brandishing rainbow flags after ambassadors from 36 countries issued a joint letter of support for the parade, and a rights survey ranked Poland as one of the weakest EU countries for legal protection for LGBTI people.

“The truth is that we do not really have any legal rights to protect,” said Jej Perfekcyjność, an organiser of the annual event, formerly a gay rights march now rebranded as an equality parade in an attempt to broaden its appeal to all minorities.

“We expect a record crowd because many people have joined demonstrations against this government in the past few months. We need a big crowd to make sure things do not get worse,” he added, aiming for a crowd of 30,000.

Last October Poland’s president, Andrzej Duda, blocked a bill that would have granted legal rights to transgender people. A few weeks later the nationalist Law & Justice party, which is close to the Roman Catholic church, won parliamentary elections and began bringing the courts under government control, leading to protests from human rights groups and scrutiny from European bodies.

Last month the government scrapped a parliamentary commission on minority and human rights. In a measure of the government’s attitude towards minorities, the minister for civil society and equal rights, Wojciech Kaczmarczyk, declared on Facebook that there should be no legal bar to private businesses turning away black customers.

Warsaw’s main annual LGBTI march was banned in 2004 and 2005 under its then mayor, Lech Kaczyński, who later became Polish president and whose twin brother, Jarosław, remains leader of Law & Justice. Since 2006 the event has taken place every year.

Perfekcyjność said there was a growing climate of fear among LGBTI people because extremist groups “feel ever more confident”. He added: “We had not seen attacks on associations for six or seven years but in the past few months there have been several cases of vandalism.”

The campaign group Lambda has taken down its Warsaw city centre rainbow flag after a window was smashed. Its advocacy officer Piotr Godzisz said it was too early to say whether attacks were on the increase.

“The official statistics show very few attacks,” he said. “Homophobia is not considered an aggravating circumstance in court. As a result, the police do not have an incentive to seek out that motive and victims do not report attacks.”