After 26 years with company A, my father was asked to relocate and they would pay for him to relocate or he could take a severance allowance instead. This was due to a buy-out/merger with company B.

My father signed a letter accepting the offer and was handed a brochure about the relocation policy. There was a paragraph about a repayment agreement that simply said-?signed at the time the offer was accepted? And ?first year ? 100% and 2nd year -50%. That?s all it said and there was no other document and nothing else to sign.
My father asked what it meant and was told that if he quit before two years he would have to pay back what they spent to get him relocated.

The company wanted him to start immediately so put him up in an expensive apartment and left my mother behind to sell their house with the help of their real estate person.

He has now been working at company B for about one and a half months and he receives a letter that said ?pursuant to the original offer of employment -sign and return this repayment agreement.

My father will not sign this document because it says he has to pay them back even if he is fired for cause and if they wanted him out, they could find an excuse to fire him and he would have to pay back the money. Remember that he was only told verbally that it meant if he quit. The form also states that by signing that he is agreeing to not file in action against the company regarding the relocation pay back.

My question is this ? Can they fire him for not signing after he?s already there, and if so will he have to pay back everything they have already spent and can they refuse to give him the severance pay they originally offered? Can they keep him there and not pay anymore which would mean my mother couldn?t move with him unless they paid for it themselves? (which they can?t afford)

A lawyer needs to read all the documents, old and new.
But meanwhile I would go to HR and just say not only wasn't I told about this but shouldn't have to agree to it, low risk though it may be. If they say they can't or won't run it by corporate, just say OK I'm having my lawyer look at it.

Personally I would not assume that there is anything nefarious going on, just legalese (to cover that one person who suddenly does something really horrible) that they didn't spell out back at the time of the offer, and take the risk that I am not going to be fired after 26 years and an expensive relocation. So I'd sign it. But that's just me.

I would take my sweet time with all of this. If they ask where it is, just say my lawyer is going over it.

First, the 100/50 clause is fairly standard. If an employee accepts a move with a relocation package, there is generally a proviso for reimbursement if the employee leaves within a certain time.

But I don't like this need for an agreement after the fact. So I would consult an lawyer about it. However, it could just be that the paperwork was winding its way through the transition team from the merger.