A report from the STUC has said firms should be legally required to monitor sectarian incidents at work.
The study comes on the same day that three Glasgow primary schools take part in a project to celebrate anti-sectarianism. The STUC report said there should also be "clear guidance" on not dismissing prejudiced comments as workplace banter or humour.
While the STUC found "real progress" in reducing sectarianism, they say it remains a force in the Scottish workplace. The report called for the development of clear anti-sectarian policies, for employers and unions to work together, and for workforces to be actively involved.
It also calls for firms to have clear procedures from removing graffiti, and for clear guidelines on how sectarianism should be reported and the penalties that will apply.
The STUC report declared: "It was worrying to learn that in 21st century Scotland examples of direct discrimination against Catholics could still be reported.
"It is also a concern that nothing was done about this in these places of employment. Trade union activists relayed these examples but they had initiated no action themselves.
"This is revealing example of the way that sectarianism can become so embedded within the culture that, although these informants disapproved of it, no opposition to its practice took place."
The research report by Strathclyde University, which was funded by the Scottish Government and the Sense over Sectarianism campaign, was published as Community Safety Minister Fergus Ewing attended an event at the Scottish Youth Theatre to mark progress in efforts to tackle sectarianism.
The minister said: "Our strategy for tackling sectarianism is based on funding key projects and bringing together organisations to work together to send a clear message throughout the country that sectarianism is never acceptable and never excusable."
He welcomed the STUC report and said the anti-sectarian group Nil by Mouth was mounting a workplace sectarianism project.
The report, by Professor Gerry Flinn, Fatima Uygun and Andrew Johnson at Strathclyde University, follows research which included the use of focus groups and interview with union officials.
One example quoted in it was said by a participant in the research to have taken place in the last five years in a well-off area where a house was on fire.
The report said: "Initially the house-owner refused to allow all personnel of the fire service to enter because he did not allow Catholics in his house.
"The leading fire officer in attendance, who was a Protestant, insisted that unless all of his crew were allowed to enter, no one would go in to extinguish the fire."
Last updated: 23 November 2009, 14:45
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