YES/ Poland and Lithuania define marriage as a union between a man and a woman in thay constitutions just as several other countries in Europe e.g. Spain, France etc. They are not mentioned here. Why? 
And Latvia not only define marriage as a union between a man and a woman in its civil law and constitution (since 2006) but also bans same sex marriages in those acts. So it is the only country in Europe to do so. (first to BANN same sex marriage, and NOT third to define marriage...)
This article sugests that Poland and Lithuania do the same. and this is not truth! So, I say about it. In my opinion, it should to be corrected.