Quorum requirements for a referendum to be valid
Poland
Answer
Optional referendum - turnout quorum
Source
A result of a nationwide referendum is binding if more than half of the number of those having the right to vote have participated in it. In case of constitutional referendum the result is always binding.
Art. 90 p. 3, art. 125, art. 235 p. 6 of the Constitution
Constitution of the Republic of Poland adopted on 2April 1997
http://www.sejm.gov.pl/prawo/konst/angielski/kon1.htm (in English - the Parliament’s website)
Comment
50% of eligible voters (however, no quorum requirement for constitutional referendum)
