Ireland's most used social networks say they will co-operate with the PSNI for "valid" investigation requests - but cannot monitor people's accounts for illegal or defamatory comments during an ongoing criminal trial.
The statement comes as the PSNI began an investigation into the illegal naming of the complainant in the Belfast rape trial on social media. Facebook and Twitter say that they do not have algorithms to scan or monitor postings while a trial is ongoing.
A spokeswoman for Facebook said that while the social media giant has automated systems in place to guard against illegal content such as child abuse imagery, the same is not in place for statements regarding ongoing trials.
Both Twitter and Facebook, which also owns WhatsApp and Instagram, have systems in place where they hand over account holders' information if they get an authorised police or legal request.
In the first half of 2017, Facebook received 77 police or legal requests in the Republic and complied with 79% of them, meaning that "some" user data was handed over.
The requests included legal probes into account information for Instagram, WhatsApp and Messenger.
By comparison, Twitter only received three requests for the first half of 2017, all of which it complied with.
Specific figures for Northern Ireland are not made publicly available by Twitter or Facebook.
However, aggregate figures for the UK show that 6,091 requests were made to Facebook in the first six months of 2017, with a 92% compliance rate of some data being handed over.
Facebook also operates what it calls "preservation requests", where it will preserve account records "in connection with official criminal investigations for 90 days pending our receipt of formal legal process".
In the first half of 2017, it received 177 requests relating to 294 Facebook accounts in Ireland. It did not disclose how many requests it complied with.
Facebook says that "each and every request we receive is checked for legal sufficiency" and that it rejects "or requires greater specificity on requests that are overly broad or vague".
The social media giant also sometimes complies with legal requests that relate to civil defamation cases.