Ulster Unionists have called on the Irish government to make full disclosure about Troubles killings.
Some families are unhappy with the amount of information provided about the 1976 IRA murder of 10 Protestant workmen at Kingsmill in South Armagh.
UUP chief negotiator Tom Elliott said the level of Irish transparency had not come close to what the UK was planning to deliver on legacy cases.
He said: "It almost gives people the perception that there is this unfair process."
He said documents coming forward from Dublin about Kingsmill provided "extremely limited" information.
The UUP met officials from the Department of Foreign Affairs (DFA) at Stormont on Thursday on legacy issues but not internal Northern Ireland matters.
The Irish government is heavily involved in efforts to restore power-sharing at Stormont.
More detailed discussions are planned about specific cases over the next week.
Two years ago, Taoiseach Enda Kenny told the families his government would provide information it held about the Kingsmill attack to a coroner for an inquest into the killings.
Mr Elliott said the British seemed to be able to get information about what its soldiers did for a host of inquests and the Irish government should be able to retrieve material about Kingsmill.
Mr Elliott added: "They have not come close to what the UK are planning to do.
"They have not shown us any willingness to do so.
"We are putting a line down at the moment that they are not coming up to what we would expect them to."
He said they were players in part of the talks.
"They have questions to answer over legacy and we will press them on that and that is the only thing we discussed today."
