Lagan was planning to buy the former Quinn group roof tile business.
The County Fermanagh business was established by bankrupt former billionaire Sean Quinn and employs about 20 people.
The Quinn Rooftiles business was being sold by Aventas, the re-branded Quinn Group.
Lagan’s chairman received a written death threat last week.
It followed a series of attacks on Lagan Group property after news of a potential deal first surfaced.
The Lagan Group told the Belfast Telegraph: “No business could operate when criminal threats against operational decisions put employees, directors and their families at risk.
“Over the past number of months we have been engaging with the local workforce and management to secure a stable and sustainable future for the employees in the former Sean Quinn Rooftiles business now owned by Aventas.
“During this time various parts of the Lagan Group (and indeed businesses not connected to the Group) have sustained a series of criminal attacks on property and plant causing substantial financial damage.
“These were executed with the sole purpose of creating a toxic atmosphere of fear and intimidation in order to illegally dissuade potential investment and investors into the area.
“We have repeatedly said that it was only a matter of time before such attacks switched their focus from property and plant to people.
“Last week, on the day his wife died, Mr Kevin Lagan, chairman of the Lagan Group, received a letter containing a threat that should the Rooftiles business sale proceed, the purchasers ‘would not live to see the benefits of the sale’.”
Since Sean Quinn lost control of the Quinn Group three years ago there has been a series of attacks on the group’s companies or those who have expressed an interest in buying them.
Kevin Lagan was sent a bullet in the post in February 2013 following plans to launch a joint venture with Quinn Building Products.
An Aventas plant was also hit with a fire bomb last month.
The company said: “The underlying strategy seems to be one of damaging value, striking fear into our employees and to discourage any genuine prospective acquirers of our businesses.”