Councils in Wales have been told they must continue to provide a proper library service even during "very tough times" for public spending.
BBC Wales contacted all 22 councils, and a number are planning closures.
As figures show book borrowing is up again, Heritage Minister Alun Ffred Jones stressed the value of libraries.
Mr Jones said the assembly government could act if an "adequate" service was not provided, but he wanted to "support and guide" local authorities.
Recent figures show that there were 681,000 "active book borrowers" in Wales in 2009-2010, an increase of 5.4% on 2008-2009, which had also recorded an increase.
More than 14.7m people visited libraries in Wales last year, which also represents an increase of 5.4%.
However, with councils facing budget cuts across Wales, there are warnings library services should be protected.
Wales' 5.4% increase of visits to library premises compares to a 1.6% decrease in England, a 1.4% fall in Scotland, and a rise of 8.4% in Northern Ireland, according to the Chartered Institute of Public Finance and Accountancy's most recent figures.
Wales was the only part of the UK to record an increase in stocks of books, up 4.4%.
Stock of audio, visual, electronic and other materials rose by 2.4%, but the number of times those services were issued fell by 2.3%.
Total expenditure on library services in Wales hardly changed, currently standing at £52.2m.
Total income dropped in Wales from £3.7m to roughly £3.3m, a decrease of 10.6%. This compares to a 3.5% drop in England, 16.1% decrease in Scotland and a rise of 55.7% in Northern Ireland.
Swansea Central was recorded as the busiest library in Wales, when measuring issues, with 590,552. Cardiff Central was second (575,143) and Llanelli third with 392,654 issues.
Swansea was also the busiest in terms of visits (485,895), with Cardiff second (439,857) and Barry County Library in the Vale of Glamorgan third with 331,595.
The figures have been welcomed by the Welsh Books Council, at a time when libraries across Wales are facing threat of possible closure as councils consider budget cuts.
Elwyn Jones, director of the Welsh Books Council, said: "The books council obviously welcomes the figures and it just shows the importance of libraries throughout Wales.
"We feel that libraries and the library service is very important, especially these days when there's so much emphasis in developing literacy."
Alun Ffred Jones, who this week officially re-opened Rhyl Library in Denbighshire following a £300,000 refurbishment, said libraries played a "valuable role at the centre of communities across Wales".
He said he did not expect libraries "to be exempt from the rigorous process that local government has to go through in facing what are very, very tough times, very difficult decisions for councils.
"But at the end of the day they have to adhere to the statutory duty to provide an adequate library service," he added.
Asked what the Welsh Assembly Government could do to stop library closures, he said: "Ultimately the government can bring sanctions on local authorities if they feel that they are not providing an adequate library service and no doubt we would do so if things came to such a pass.
"But in the main we would see ourselves as supporting and guiding local authorities so that we don't reach that very unfortunate situation."
BBC Wales contacted all 22 local authorities in Wales, although some have not responded.