Union not enforcing its own contract

I was recently fired from my job. I was givin termination papers that were not proper.  The company by contract has 10 days to give me "proper" termination papers per my union contract. I Grieved my termination and the termination paperwork. At my local level hearing the company upheld my firing but also gave me new amended termination paperwork. The company knowing the termination paperwork was improper. The problem was that the new paperwork was also improper because it was after the 10 day window.  At my state level hearing the panel of 2 company men and 2 union members agreed that the 2nd letter was impropper due to the time issue. The then upheld the original termination papers even after the company basically admitted that the paperwork was improper by amending the paperwork after the 10 day window. My question is how can the union not uphold its contract when I am a member in good standing with the union, and can I sue my union for not follwing the contract.

If you are employed in the private sector and your employer is covered by the National Labor Relations Act, you can file an unfair labor practice charge against your union with the National Labor Relations Board.  However, based on the details of your posting, the union seems to have upheld the contract, it was the decision of the grievance board that decided the termination was appropriate despite your contention that the original notice was improper.