Delegates refused to allow a vote which would have backed three motions calling on the union, representing 80,000 members, to support the repeal of the Eighth.
On Thursday, the general secretary of Ictu Patricia King urged the 800 delegates to take part in the plebiscite on May 25.
Fórsa was expected to back calls for a yes vote.
During three motions on public policy calling on Fórsa to support repeal, there were highly emotional contributions from both sides.
The three motions were remitted following a vote, while a fourth, calling for a respectful debate, was put to a vote and carried.
There were calls for Fórsa to have “the backbone” or courage of its convictions, saying there was a week left to undo the damage of 35 years.
Delegates from the floor grew angry at Sligo “no” voter Francis McHugh after he asked who was going to fund the legalised abortions — most abortions in the UK were funded by the taxpayer, he claimed.
There were shouts of “shame, shame”.
He was again shouted down from the floor when he said rape was horrific, but its horror was increased where there was legalised, unrestricted abortion.
However, there was sustained applause for a personal story from a father whose daughter would have been 10 last Christmas, had she lived, and who said women should never be forced to travel from their own country and bring their babies home in boxes on Ryanair.
James Kavanagh of the Schools Completion Programme branch said this first conference of Fórsa was to be “a unity conference”.
“I firmly believe they are fundamental issues, but they are not core business for Fórsa,” Mr Kavanagh said.
In the end, the delegates agreed.
However, union sources said the result was a huge surprise and the motions asking the union to support the repeal of the Eighth Amendment were expected to be voted upon and carried.
Meanwhile, motorists in a border county were left stunned at the sight of more than 17,000 white crosses along a large stretch of roadway.
@declanganley @loveboth8 @Together4yes @prolifecampaign @Colmogorman 17,000 white crosses to represent the lives that will be taken per year in Ireland if there is a yes vote! Road from Bridgend to letterkenny Donegal pic.twitter.com/x3SWvxGJwG
— The 8th and my Irish Identity (@ToRetain) May 18, 2018
The crosses, which were placed a metre apart, were believed to have been placed there by the no campaign in advance of next Friday’s referendum.
The crosses extend from Letterkenny in Co Donegal to the village of Bridgend on the Derry border, a distance of approximately 30km.