The company has confirmed that 250 jobs will be cut as the UK operations of the three ISPs are merged into one unit, which will be called Tiscali UK.
The integration of the three businesses means a "reorganisation" of staff, "to eliminate overlap or duplication of roles and improve operational and cost efficiency", the company said.
The cuts will affect all areas of the businesses, including content, finance, IT and human resources.
Tiscali bought LineOne, which was previously owned by BT and United Business Media, for €100m (£60.1m) in April. This was a fraction of the original €400m (£240.5m) asking price.
The company bought Dutch ISP WorldOnline in December and French rival LibertySurf in January. The purchases made Tiscali the fourth-largest ISP in the UK and the second-largest in Europe, with a registered user base of 16m.
The company also announced that Sergio Cellini, formerly chief executive of Excite Italia, will become chief executive of Tiscali UK.
The UK operations of WorldOnline include the assets of what was bun.com, the ISP launched by The Sun newspaper in April 1999. Bun.com, originally known as currantbun.com, was bought by WorldOnline for an undisclosed sum in March 2000 and closed shortly afterwards.
www.tiscali.com