Of course you're not allowed to invite anyone to the wedding, you're not getting married! IMO, regardless of who is providing the finances, the bride and groom should decide the guest list for their nuptials, with suggestions from both sets of parents. To me, giving your kids a monetary gift to help with some or all of their wedding doesn't not entitle someone to make all the decisions. Similarly, not providing any financial contribution doesn't mean that a parent can't offer opinions/suggestions etc.
And when did this conversation take place? 5min ago? Why haven't you been able to speak to your son as yet?
I think it's a bit overly dramatic to say that you don't want to attend your son's wedding because of some perceived slight. But if that's all it takes for you to want to miss out on this important event, I think you should skip it. It's very petty and kindergarten-esque, but by all means, take your toys out of the sand box and don't play with those people again.
I hope you can help. I understand your son's wedding was a couple years a go but I'm going through a similar situation and I would like to know how or if the situation got resolved? My son who is 22 is getting married this coming July I don't even know the date, We live in MD and her family lives in CA. but she wants to have the wedding in Vermont.Her family cant help pay but they are giving her all this suggestions on how and where to do this. we are expected to pay not only for the wedding but to get her family and ours to the place. I don't even know the date of the wedding I was told by her we needed to help then pay. I talked to my son and asked him to talk to her about changing the location so our family could attend the wedding we are paying for but apparently he has no voice in this event just a check book.