The phrase "effective veto" means having the power to reject or block a decision or proposal, ultimately having the final say in whether something can happen or not. Full definition
First Minister Nicola Sturgeon has been arguing that the draft clauses do not provide «a general power to create new benefits in devolved areas as was promised by the Smith Commission and gives the UK government effective veto over changes to universal credit, including bedroom tax.» (theconversation.com)
Conversation has so far centered on how the need for a supermajority consensus in network decision - making means that any mining pool with enough hashing power holds effective veto power over any proposal, a fact many believe is responsible for delays in SegWit adoption. (getrevue.co)
That's why a relatively small group of hardcore anti-clean energy climate skeptics in the right - wing base has exercised effective veto power over American climate policy: they have the intensity and they're backed by money. (grist.org)