Can a country block its airspace to international civil flights without any reason?

Suppose, a country 'X''s civil airline wants to fly to another country 'Z'. There are three routes. However, the shortest route is 1000km which is through country 'Y'.

Can the country 'Y' block its airspace for civil airlines of 'X' without giving any reason?

If NO, can 'X' go to an international court for this? If YES, what would the penalty for the country 'Y' be?