MADRID - The European Commission warned on Tuesday that Spain's large-scale migrant regularization must not produce "negative consequences" for other EU member states, as the initiative is expected to legalize the status of half a million migrants.

The commission's statement came during a plenary debate at the European Parliament, where EU Commissioner for Internal Affairs and Migration Magnus Brunner underscored that migration is a shared challenge for all member states, and decisions taken by one country should not adversely affect others.

A residence permit "is not a blank cheque" for unrestricted movement across the bloc, Brunner said, reiterating that while national regularization policies are allowed, there are clear EU rules governing free movement and residence.

If beneficiaries of Spain's regularization measure are found to be living illegally in another member state, they "must return to the country where the permit was granted," he added.

The commissioner also stressed the need for a strategic, secure, legal and controlled approach to migration across the EU, warning that irregular migrants should be returned under existing regulations.

The Spanish government, led by Prime Minister Pedro Sanchez, approved a plan in late January to provide legal status to roughly 500,000 undocumented migrants. The move has drawn scrutiny within EU institutions and among other member states for its potential impact on broader European migration management.