Phone hacking victims including Gerry and Kate McCann, the parents of missing Madeleine, have written to the prime minister accusing him of backing down on press reform promises.
In an open letter to David Cameron, the hacking victims express "frustration and dismay" that commitments he made to implement a cross-party agreement on press regulation.
They also say that while Mr Cameron has met regularly with the owners and editors of several newspapers - including Rupert Murdoch - their own requests for a meeting have been ignored.
The letter follows a government decision to shelve planned legislation that would require news organisations to pay their own legal costs as well as the costs of the complainants, even if the media company wins the case.
The rules, recommended by the Leveson Inquiry into phone hacking, were part of a cross-party agreement made in 2013 aimed at newspapers that opted out of a new regulatory structure in favour of self-regulation.
At the end of last year by John Whittingdale, the culture secretary, said he felt it was not the "right time" to introduce the rules.
In their letter, the hacking victims say they were "disappointed" at Mr Whittingdale's comments and that "by delaying or shelving this measure your government will deny the public the low-cost access to justice that Leveson intended".
They also calls on Mr Cameron to confirm that the second stage of the Leveson Inquiry into phone hacking will go ahead.
The first stage of the inquiry reported in 2012.
The second stage - intended to examine the links between journalists, politicians and the police - has faced delays and there have been uncorroborated reports that it could be abandoned.
In their letter, the hacking victims write: "We urge you now to remove any doubt by confirming that the second phase of the Leveson Inquiry will go ahead without fail once the last criminal trials have concluded."
Alongside the McCanns, other signatories to the letter include Christopher Jefferies, a retired schoolteacher who was wrongly accused of murder by multiple newspapers in 2010.