Europeans will from the middle of next year be able to use their domestic mobile data subscription across EU member states without paying any extra fees, no matter how long they travel for, the Commission said Wednesday.

However, there will also be mechanisms to prevent “abuse,” meaning people will have to use SIM cards from the countries where they live, or from countries with which they have “stable links.” It’s not yet clear to what degree people will need to prove these links, or how.

Get Data Sheet, Fortune’s technology newsletter.

The Commission has for years been promising to wipe out roaming surcharges, as it tries to create a true digital single market. Its efforts have resulted in a gradual phasing-out of these surcharges, and June 15, 2017, was the point where everyone had agreed people would be able to use their phones across the EU as they do at home.

However, this agreement came with a vague “fair use” clause, designed to protect mobile operators from losing money, and earlier this month the Commission sparked outrage when it said what it thought fair use should entail.

The Commission said mobile operators should be able to place limits of at least 90 days on their customers’ surcharge-free data roaming while in other EU countries.

Days later, Commission President Jean-Claude Juncker forced his vice president, Andrus Ansip, and digital economy commissioner, Günther Oettinger, to make a humiliating climbdown—they had to withdraw their proposal and go back to the drawing board.

The new proposal comes with no limits on time nor on data volume, but Ansip and Oettinger said Wednesday that they would let operators “intervene if they detect abuse.”

Operators will be able to charge their customers small extra fees for roaming if, for example, they note that they hardly use any mobile data while at home, but loads of data while roaming. The “subscription and sequential use of multiple SIM cards by the same customer while roaming” will also be seen as suspicious.

The problem is that operators in some countries, such as the Baltics, charge customers as much as five or six times less than those in others, like in Germany or Belgium.

Ansip said the Commission wanted to stop people from “buying packages of SIM cards from a cheap country and selling in countries where packages are at a much higher level.”

For more on the EU, watch our video:

What’s more, a “sustainability clause” in the new proposals will allow mobile operators suffering losses under the new system to “ask for derogation to stay out of the system.”

If these proposals go through—the European Parliament still has to discuss them, and there’s been no fresh impact assessment—then they will create a lot more work for the EU’s telecoms regulators.

National telecoms regulators will have to settle complaints from users who disagree with being charged extra for roaming by their operators.

They will also have to field complaints from operators about people trying to resell foreign SIM cards in bulk. And, if an operator wants to opt out of the whole scheme, they will have to provide evidence to the regulators that their domestic charging model is being put at risk by “roam like at home” hyperactivity.

And as for the digital single market, it appears mobile operators are for now shielded from the market becoming too unified for their bottom line.