He had initially requested they join up after next weekend's penultimate round of EDF Energy Cup fixtures.
All the regions though, could find themselves chasing semi-final places when the pool stages conclude between October 31 and November 2.
And they have now issued a strongly-worded statement signed by Ospreys duo Roger Blyth and Mike Cuddy, Scarlets chief executive Stuart Gallacher, Newport Gwent Dragons' Gethin Jenkins and Cardiff Blues' Bob Norster.
The statement read: "Given the absence of meaningful dialogue with the Welsh Rugby Union to date, it has become apparent that reaching agreement on extended player release, at least in the short-term, is unlikely.
"The regions remain as committed as we have ever been to Welsh rugby. "Last season, during World Cup year, as the WRU's own figures show, the regions released players for national duties for a combined total of 198 days, despite only being required to do so for 104 days.
"In return, the WRU have displayed contempt for the regions, offering and then reneging on agreements, arbitrarily shifting goalposts and, latterly, asking us via the national coach to effectively overlook the EDF Cup.
"However, all of these issues could be holistically addressed and resolved in the future through a new participation agreement, as the Guinness Premiership clubs and RFU (Rugby Football Union) have so successfully demonstrated in England."
The WRU have yet to respond to the regions' comments, although WRU chairman David Pickering claimed talks between both parties were on-going.
Gatland, who led Wales to RBS 6 Nations title and Grand Slam glory during his first five games in charge last season, is due to name his autumn Test squad next Tuesday.
After South Africa, Wales host Canada, followed by Tri-Nations champions New Zealand and then Australia.
And an uneasy political situation at the top end of the Welsh game will inevitably overshadow the build-up to those matches.
The regions and WRU are also engaged in drawing up a new so-called "Participation Agreement," given the current agreement between them runs out next May.