Porterfield - Chose County Over Country.
Counties have been warned that a reluctance to release players for international duty with lesser nations comes "at their peril".
The International Cricket Council and England and Wales Cricket Board have determined to get tough to protect the integrity of matches played by the likes of Ireland and Scotland.
There has been concern that these countries may have to field under-strength sides if their county-contracted players are unavailable.
Counties have been generally willing to release players but the governing bodies do not want players to feel they may be jeopardising their careers by turning out for their countries.
Next month six of the ICC's 'associate' countries - Ireland, Scotland, Bermuda, Canada, Kenya and Holland - will play for three places at next year's World Twenty20 at a tournament in Belfast.
ICC president David Morgan said: "In terms of the ICC WT20 qualifier, that will make sure the best teams reach next year's event, rather than the teams with the most top players available on that weekend in August, something that will then have a knock-on effect of enhancing next year's event."
ECB chairman Giles Clarke insisted the English game's governing body were firmly behind the policy.
Clarke said: "The ECB recognises that nation versus nation is the lifeblood of cricket and its integrity must be protected at all costs."
In summarising their stance, an ICC statement added: "It has further agreed that all parties compromise or fail to protect this belief at their peril."
Ireland have recently been affected with the likes of William Porterfield and Niall O'Brien opting to stay with Gloucestershire and Northamptonshire respectively rather than play against Bangladesh A.
The ICC stress players will always have the freedom to make their own decisions but do not want clubs putting undue pressure on them.
Cricket Ireland chief executive Warren Deutrom said: "We would actively like our players to develop in county cricket because it means when they are released back to us they are better players.
"At the moment they can't make a career playing in Ireland.
"So this is a very tough one for the players, and at the end of the day it comes down to them.
"This is welcome news. It is a complicated issue but hopefully there will not be pressure.
"We do not want to get to point where someone would have to retire from international cricket."