Their announcements come after plans were announced earlier this week for a new Rugby Champions Cup next season spearheaded by the leading English and French clubs.
Premiership Rugby and Ligue Nationale de Rugby are forging ahead with their own blueprint, having also extended an invitation to Celtic and Italian teams to join them.
In a statement which echoed those by the WRU and the IRFU, the SRU said: "Scottish Rugby wishes to clarify that its clubs will not be participating in future tournaments which do not have the full approval of the International Rugby Board or the relevant national rugby unions. Scottish Rugby and its clubs remain fully committed to the development of a pan-European rugby competition and we welcome the recent comments made by the IRB chairman, who confirmed that a pan-European tournament remains the goal of the IRB. We are confident this can be achieved.
"Scottish Rugby remains committed to working with our colleagues across Europe and encourages all parties to fully engage in meaningful negotiations. We hope that negotiations can be concluded quickly."
The French Rugby Federation have also said they would not support any new Anglo-French competition.
Mark McCafferty, Premiership Rugby chief executive, confirmed that England's six qualified clubs - Leicester, Saracens, Gloucester, Harlequins, Northampton and Exeter - will be represented at this season's English and Welsh Heineken media launch in Cardiff on Monday.
But, looking further ahead, he said: "We are certainly not attending the meetings on October 23 and 24 that we have been invited to, and the French clubs aren't either. As far as we are concerned we are not in ERC [European Rugby Cup] competitions, and neither are the French clubs.
"From our perspective, those competitions in their current form are over. We don't have any dispute with ERC, from our point of view, which is why the appointment of a mediator [Canadian lawyer Graeme Mew] by ERC is a bit odd. We've served notice, we are discharging all of our obligations during that notice period, and at the end of that notice period we will go to play in new competitions. There is no dispute about that from our point of view."
McCafferty said that he fully expected the RFU (the English union) to support their actions.
"We are putting a competition format and a financial structure in place through the Rugby Champions Cup that is going to be attractive to everyone participating in it.
"We believe, as we've said, that quite a number of teams want to be in the Rugby Champions Cup, so we will continue working through the working group to put in place the remaining details in October of the competition. We accept we need then to present it as an option or invitation to others as to whether they want to be part of that or not. If people do, great, and if they don't - or they are not allowed to be part of it - then they must make their own decisions.
"Teams will want to be in this competition, particularly if it's commercially attractive. They may well need their union's support on that, but frankly if there is no viable alternative then people want to be part of what is a strong option that is on the table.
"We are looking to pull final details together by the end of October. We need to know within that time frame whether people are in or not in. The door is open for others, and we would want others to be involved so we can have a broader European competition."