The governing body made the announcement they were reverting to a two-tier funding model amid reports it intends to cut a professional team.
The WRU has neither confirmed nor denied if reducing the amount of sides from four to three is part of its plans.
Neath and Swansea East Labour MP Carolyn Harris said this was “totally unacceptable” and accused the WRU of failing to answer “fair questions” about the future of the clubs.
Harris, who is also deputy leader of Welsh Labour said she was “really disappointed” about the decision.
“I, and my fellow MPs in the region, are all intending to take action to knock some sense into the WRU because we can’t lose either the Scarlets or the Ospreys.”
Harris said the pride and community work the clubs provided was “as important” as the game itself.
She added that every MP from the two regions, “regardless of political affiliation” would contribute to a strongly worded letter demanding a meeting and the current feeling among politicians was that this was a “really bad decision”.

Torsten Bell, MP for Swansea West added:
“The uncertainty created by the Welsh Rugby Union’s statement on Sunday about the future of regional rugby is bad for everyone – fans, clubs, and the communities around them.
“The WRU must answer the legitimate questions being asked by the Ospreys, and for that matter, the Scarlets, so that everyone can move forward in the best interests of Welsh Rugby.
“I’ll be meeting with the club CEO in the coming days to discuss the urgent matter and will be monitoring developments closely in the weeks ahead.
The four regions were given a deadline to sign the new PRA by 8 May, but only WRU-owned Cardiff and privately-owned Dragons put pen to paper.
Last week, Ospreys and Scarlets said they had asked the WRU for assurances that the takeover “will not disproportionally benefit Cardiff and disadvantage the independent clubs”.
After Ospreys and Scarlets had not signed, WRU have served a two-year notice on the current agreement that underpins the Welsh professional game.
That current PRA runs out in 2027 although it was due to be superseded by the new five-year deal.

Nia Griffith MP for Llanelli yesterday also spoke about the shockingly poor manner and timing of the annoucement. She said:
“The announcement on regional rugby funding from the Welsh Rugby Union over the weekend, with little consultation or detail as to what is to follow next, has generated nothing but chaos and uncertainty.
“Leaked the night before, but with only one minute’s notice to the regions affected before the WRU issued their official statement on Sunday, the manner in which it was made was shockingly poor.
“It has left both Scarlets and Ospreys Rugby, in particular, to pick up the pieces and move forward in the most positive way that they can.
“I attended a grassroots rugby event at Parc Y Scarlets yesterday and met with Jon Daniels, Scarlets Managing Director, to pledge my support as they fight to ensure top level rugby still has a secure home here in Llanelli and West Wales.
“The WRU now need, as a matter of urgency, to work constructively with all four regions to deliver an agreement that safeguards professional rugby here in Wales in a way that works for all parts of Wales.
“Both on and off the field, the Scarlets have a huge role to play in the future of Welsh rugby with its history, tradition and rich resource of players, coaches and supporters and its position as a gateway into the game for West Wales.
“We are justifiably proud in Llanelli of our rugby heritage and of the role that the Scarlets can play in helping Welsh rugby recover its position on the European and World stage.
“Our town and region can and should be an important part of any solution.”
The WRU is scheduled to meet with representatives of Ospreys, Scarlets, Cardiff and Dragons on Wednesday at a meeting of the Professional Rugby Board (PRB), which is responsible for running the professional game in Wales.
A spokesperson for the WRU said they “would welcome engagement with the local MPs and look forward to the discussion”.
[Lead image: Ospreys Rugby]
