Suppose i am married with a earning wife. We both earn the same. I am only son of my parents and she is also only issue of her parents. Now as i have to look after her expenses and also my children i can hardly give 10% of my earnings to my parents. But my wife gives all her salary to her parents as she need not to give any money to run our family according to Islam. So i cant help my parents as much as she can. Isn't this a injustice to me or my parents? Why my parents will get lesser from me just because almighty gave them a son not a daughter?
Well your question could have two possible aspects: the POV of shari'a and the aspect of partnership (this is also a more or less of Shari'a POV) and the love and mercy between husband an wife.
From a sharia'a point of view:
it's clearly the husband who has to support his family even if the wife is working (for example in Quran), but as good as he can. This means if he is poor he isn't asked to support his family above his possibilities. And the same situation is when taking care about your parents you'll have to support them as good as you can!
Therefore at first place you have no right over your wife's salary and she and your children have the right of being supported by you!
According to the following Fatwa (Arabic) a wife is neither asked nor should be forced to support the family of her husband even if she was wealthy. But she could do it to gain reward أجر by Allah.
I would be glad if someone could add information supporting that this isn't an injustice, or maybe I'll try to edit this answer and if i found enough information and arguments to explain this.
But now we come to an other Point:
A few words about Marriage in Islam
When we read in Quran the Verses about the relationship between husband and wife and family matters we always find the words "و ان خفتم" ="And if you fear that ...".
This means that as Allah brought you together in love and mercy both of you should care for an other and try to forgo or at least be kind to each other as we can conclude by reading Quran Verses line in Surat an-Nissa' and Surat ar-Rum. And as there are duties of a husband there are also duties of a wife. But the most important thing is (And do not forget graciousness between you وَلَا تَنْسَوُا الْفَضْلَ بَيْنَكُمْ) which is stated in a Verse talking about divorce. But the word الْفَضْلَ means more the graciousness in Arabic: it's something above the usual this means in such a relationship each partner should try to give his counterpart (if possible) much more then he would expect from him!
So yes according shari'a no right over your wife's salary, but if you live in a true relationship this shouldn't be a problem if you both are neither selfish nor having negative feelings for each other because of this matter.
In my case Alhamdulillah we passed true a very bad (financial) situation and my wife and even her family helped me out (without me asking her) and would do it at any time if i asked her and vice versa! In a relationship each part should have his/her goals but never forget that there are common goals whom will need both parts to co-operate!
And Allah knows best!