Rupert Murdoch has stepped up his attack on tech companies such as Google and Facebook over their increasingly dominant market position, which is eating into the revenues of traditional publishers such as News Corp. and undermining their business model.

In a message to shareholders published in News Corp's annual report released on Wednesday, the octogenarian media tycoon vowed to continue to contest the "abuse of the marketplace" by some big tech companies "wherever possible".

Rupert Murdoch has vowed to continue to fight the threat coming from tech giants. Credit:AP

"This is an era where publishers – and the economy and society at large – are affected by the behaviour of a small number of technology companies," Mr Murdoch said.

Without naming the companies, he said the tech giants were "using their dominance to the detriment of many".