Leaders of the world's major economies are planning a co-ordinated crackdown on people and corporations that evade taxes and shortchange public coffers.

The Group of 20 countries agreed to share tax records by 2015 as part of a pledge to crack down on individual tax cheats and global corporations that use complicated arrangements aimed at paying as little tax as possible.

The topic of taxation in a global economy has become a key political issue as multinational firms such as Apple and Starbucks face scrutiny about their low tax bills from the countries in which they make most of their money. Investigative reports into the use of offshore tax havens by the world's wealthiest individuals have added weight to the view that governments are missing out on much needed revenue.

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As business increasingly moves online and international, the cash-strapped governments approved an aggressive timeline to adopt the automatic sharing of tax information. The deal was solidified after China, the last holdout, agreed to the plan just days before the summit in St. Petersburg.

"We are committed to automatic exchange of information as the new global standard," said the G20 final communiqué. Member countries will work out the details of the plan throughout 2014 with the goal of having the system in place by the end of 2015.

Prime Minister Stephen Harper called the tax exchange agreement "extremely positive," even though concerns remain to be addressed. "Obviously, there are many details to be worked out," he said. "I think we'll find as we go forward in discussions that those kinds of difficulties, or potential difficulties, those concerns will also be shared by a number of our partner countries so I'm confident that we can move forward on this in a way that's positive for everyone."

Albert Baker, national tax quality and risk leader at Deloitte LLP in Canada, said the information-sharing agreement is part of a broader package of sweeping potential new tax reforms endorsed by G20 leaders Friday. Many of the key initiatives are being developed by the Organization for Economic Co-operation and Development to harmonize tax policies globally.

"For multinational companies around the world, this could result in dramatic change," Mr. Baker said.

He said many countries have tailored their laws to attract business in certain areas – such as tax-friendly patent rules – and could face pressure to unwind their special structures. "The G20 supports it in principle, but it will be interesting to see over the next two years … whether the necessary level of co-operation among countries can in fact be achieved," Mr. Baker said.

Arthur Cockfield, a law professor at Queen's University in Kingston who studies international tax agreements, said the countries involved must be clear as to how the information will be protected.

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"Governments will more effectively engage in automatic tax information exchanges if they have assurances that the transferred information will be protected by laws that are similar to their own laws that protect taxpayer rights," he said. "This should help overcome concerns when taxpayer information is transferred to countries such as Saudi Arabia, Russia and China, that may not have traditionally protected taxpayer rights to the extent expected under Canadian law."

Fred O'Riordan, tax policy leader at Ernst & Young LLP in Toronto, said it should be possible for G20 countries to share tax information because there are already many cases of bilateral information sharing, and countries have developed privacy standards with each other.

"Of course, the wider you cast the net, the more risk there could be leaks of information," Mr. O'Riordan said, "but I think all of the parties participating are well aware of those risks and are going to be implementing measures to safeguard privacy."

Domenico Lombardi of the Waterloo, Ont.-based Centre for International Governance Innovation, said the 2015 timeline is "ambitious" and questioned whether it will be met. "This is done on purpose to escalate pressure," said Mr. Lombardi, who attended the G20 summit as an observer.

A proposed U.S. law requiring foreign governments – including Canada – to report banking information involving U.S. citizens has already run into concerns from the Canadian government and attracted the attention of Canada's privacy commissioner.

Questions of privacy will likely increase given that the G20 includes non-democratic countries where human rights are a concern, including China and Saudi Arabia.

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While the political attention in St. Petersburg has focused on the crisis in Syria, the G20 released numerous pages of communiqués, action plans and annex reports on their economic plans. Among the key points:

The G20 noted improved growth in the U.S., Japan and Europe, but that global growth prospects have been marked down repeatedly over the past year.

"Despite our actions, the recovery is too weak, and risks remain tilted to the downside. In the last months financial market volatility has increased," the G20 stated.

On monetary policy, the G20 noted the concern that actions by some countries can lead to unintended negative consequences elsewhere.

"We commit to co-operate to ensure that policies implemented to support domestic growth also support global growth and financial stability and to manage their spillovers on other countries," it stated.

In an accompanying "action plan," report, The U.S. Federal Reserve – where its quantitative easing policies have caused concern within the G20 – issued a statement on its plans.

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"The Federal Reserve intends to continue its asset purchase program and employ its other policy tools as appropriate until the outlook for the labour market has improved substantially in a context of price stability," it states.