- Price stability. The inflation rate should be no more than 1.5 percentage points above the rate for the three EU countries with the lowest inflation over the previous year;
- Budget deficit. This must generally be below 3% of gross domestic product (GDP);
- Government debt. The national debt should not exceed 60% of GDP, but a country with a higher level of debt can still adopt the euro provided its debt level are falling steadily;
- Exchange rate. The national currency's exchange rate should have stayed within certain pre-set margins of fluctuation for two years (no re- or devaluation of currency);
- Interest rates. The long-term rate should be no more than two percentage points above the rate in the three EU countries with the lowest inflation over the previous year;
So far the criteria have been important for countries willing to adopt euro since it's a precondition for joining (this statement is conditional itself as seen from history). For joining countries it is a good motivational exercise to get their finances in order. Once already in the eurozone motivation quickly disappears.
So how should we deal with that? Shall we fine the countries that are not capable of cut their spending (read: living within their means)? That's like asking for money from a beggar so it probably wouldn't work. There are still couple of things that could be tried.
Make it political! The main reason for not cutting spending or increasing spending for politicians is the support of their voters. Political promises can often lead to overspending so there is motivation for politicians to spend more than possible. So why couldn't it be possible to force the government step down if two out of five criteria are broken for example?
Another idea is to keep away the cookies. Today a lot of countries are receiving structural funds and richer countries are participating in other mechanisms like Framework Programme. Would it make sense to cut funding for countries that aren't fulfilling their duties? Since all of the EU countries aren't in the eurozone it would be impossible, but approach as such would serve its course (as can be seen in Greece today).
I would prefer stabilizing the eurozone with political measures which reduces populism, the mother of all wrongdoings. We should remove the motivation to behave badly, fines and nagging doesn't work here!