Groups B and C were more of a reserve team, with guests in these groups not actually able to attend the wedding unless someone in group A made a spot available.
"Please keep a close watch on our wedding website for notice that we have space available," the invite instructed.
But if guests in groups B and C already knew they couldn't attend they were told "it is helpful that you decline via the RSVP function on our website".
The bride and groom also said they "encourage our guests to hire a babysitter" and "leave your children at home".
"As much as we love your kids, we are doing our best to make space for all of the guests we can," the letter explained.
"We also ask for our single guests to forgo their plus one if possible."
The invite was retweeted more than 1400 times, with some describing it as "tacky" and "rude".
However some said the invite's grouping of guests onto waiting lists and limiting plus ones was understandable, given social distancing measures meant couples could only invite a certain amount of people.
In the UK, couples are allowed to have up to 30 people attend their wedding and will be able to have 30 people at the reception from August 1.
Weddings also have to be "Covid-secure" meaning social distancing between different households must be followed, group singing and playing of instruments are strongly discouraged and ceremonies should be kept as short as possible.
In Australia restrictions around weddings and the number of guests vary from state and territory, with all regions except for locked-down Melbourne and Mitchell Shire able to have ceremonies and receptions.
