The 30 SFL clubs on Tuesday received a document in which Longmuir reportedly argues that Rangers and Celtic reserve sides should join the lowest league in any new structure so that the Glasgow clubs would continue to have a presence in Scottish football if their top teams move elsewhere.
The development came 24 hours after the Scottish Premier League announced their clubs would vote on plans for a merged 12-12-18 structure on April 15, with a view to introducing it next season.
SFL clubs have not set a date and have also been discussing plans for a 12-12-10-10 league, which would require two new teams, and Ritchie feels they should focus on the plans in hand rather than creating fresh controversy.
The Falkirk chairman told BBC Radio Scotland's Sportsound programme: "The problem I have with it, I think at this stage it's just a total distraction from the key issue that everybody is discussing, which is reconstruction. There are pros and cons with it but it is clearly going to be a contentious issue.
"It's going to divide the clubs and it's going to divide the supporters and to introduce it at this stage of the reconstruction debate, I think it's irresponsible. I got it absolutely out of the blue this afternoon when I opened my emails."
Ritchie added: "Maybe there's an opportunity after reconstruction to look at the pros and cons and decide if it's a good idea, but at the moment we have very tight timescales.
"The SPL have said they are going to vote on the 15th of April. The SFL are behind that, partly because it was the SPL that were drawing up the documents.
"But the SFL have got quite a lot of catching up to do and to suddenly put a new variable on the table, and one that will certainly divide the clubs and the supporters, all that is actually doing is putting the whole process into further disarray."
The plans do not appear to have been shared with the SPL and St Mirren chairman Stewart Gilmour expressed his club's opposition, saying: "Our view has never changed on colt teams. We have no desire to have some clubs having colt teams and others not, it's as simple as that."