Are referendum results binding?

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)