The Reserve Bank of New Zealand's commentary accompanying its rate hike fired up speculation it could intervene to push the New Zealand dollar lower.Some economists said the strength of the comments, in particular the use of the word "unjustified" suggested intervention to sell the New Zealand dollar was now more likely. Westpac chief economist Dominick Stephens said the Governor's comments were a direct warning that the bank may intervene to sell New Zealand dollar within days."We interpret this choice of language as a direct warning of intervention," Stephens said.Other economists were less sure, saying intervention was less likely, although it could not be ruled out.If so, it will need to be done in a targeted manner. At present the RBNZ has approximately NZ$8.4bn in foreign currency intervention capacity available to it, according to Credit Suisse analysis.The Reserve Bank operates a "traffic light" system for deciding when to intervene. The currency must be at 'extreme' and 'unsustainable' levels, and the Reserve Bank must be able to intervene in a way that catches the market off guard at an 'opportune' moment. Any intervention must also not clash with the bank's monetary policy moves. The Reserve Bank's comments were seen as satisfying the extreme and unsustainable conditions, while the pause in the rate hike cycle is seen as opening the door for intervention that did not clash with a tightening."On the face of it, 'unjustified' opens the door to currency intervention," ANZ Chief Economist Cameron Bagrie said."We're not convinced the trigger will be pulled. It's more likely we'll see covert and passive action as opposed to open intervention, but we're on notice," he said.The Bank has previously indicated that if it acts in the market it will likely be in the NZD/USD currency pair, given its greater liquidity. And if it does so, it will pick a time when trading is thin in its home region, such as a public holiday in Australia, suggested Sean Keane of Triple T Consulting, in a note to clients on behalf of the Credit Suisse Singapore Branch.  The next Australian public holiday is on Monday 4 August. "We should expect to see Messrs Wheeler, Spencer and McDermott all making increased reference to the unwelcome level of the currency as the run up to any intervention," observed Keane. If they're very successful, a real intervention may not be necessary at all.