Libraries in Dungannon and Coalisland have seen their opening times cut by a total of 12 hours less every week.
Since April last year, Dungannon Library, which is one of the most modern in Northern Ireland, opens to the public 50 hours a week, compared to 57 in 2014.
The library in Coalisland, meanwhile, provides a service for 35 hours a week at present, which represents a cut of five hours.
In Cookstown, library users have seen opening hours cut from 57 to 45 since April 2014, while in Magherafelt, the library opens 45 hours every week compared to 48 last year.
Fivemiletown Library will see its hours remain the same, at 18 a week.
Details of the new opening times were revealed as the Board of Libraries NI approved its proposed policy on the issue.
The policy explains how library opening hours are established and sets out the revised opening hours for each library which will take effect in October of this year.
A spokesperson for the organisation explaibed: “Libraries NI held a public consultation on the proposed Opening Hours Policy and proposals and was pleased to receive almost 4,000 responses.
“The policy involves all public libraries being categorised into bands based on level of use, with the revised opening hours reflecting this use.”
Professor Bernard Cullen, Libraris NI Chairperson, said: “The Board recognises that reducing opening hours reduces access to services and will impact on library users. This decision has not been taken lightly and is a better option than closing libraries.”