More than a quarter of people in Northern Ireland would object to living beside a gay neighbour, a new survey said.
Negative attitudes towards travellers and people with disabilities have also increased, research for the Equality Commission suggested. Views have hardened against people from different backgrounds, including race, disability and sexual orientation, during the last six years.
A group representing the gay community said they were being treated as "second-class citizens" after the survey highlighted 30% of those asked overall felt some form of prejudice was acceptable.
The commission's chief commissioner Michael Wardlow said: "This is a worrying insight into the population's psyche and proves that much work remains to be done to break down barriers in our mindsets to create a fairer and more equal society for everyone in Northern Ireland."
The most negative attitudes were towards travellers. Last year, 35% of those asked would mind having a traveller as a work colleague, 54% against having one as a neighbour and 55% against having a member of that community as an in-law. This compares with 38% as a work colleague and 51% as a neighbour or in-law in 2008. Negative attitudes towards people with disabilities have also increased.
The commission's study said more than a quarter of people (27%) would mind a gay, lesbian or bisexual person living next door, compared to 14% in 2005, with 42% unhappy about them becoming an in-law, a rise of 13 percentage points over the last six years.
Around a third of people (35%) would mind a transgender person as a work colleague, rising to 40% as a neighbour and 53% as an in-law. This is the first time a major survey in Northern Ireland has considered attitudes towards this group.
John O'Doherty, director of the Rainbow Project which lobbies for gay rights, said the report provided startling information. "What this report clearly shows is that not enough is being done to address the negative perceptions that exist against lesbian, gay, bisexual and transgender people," he said.
The survey involved more than 1,000 interviews with members of the public across Northern Ireland conducted during last September.
Negative attitudes towards those experiencing mental ill-health increased more over time than attitudes towards any other group. People were least likely to mind having someone of a different religion or with a learning disability as a work colleague.