The European Commission is calling on the EU Court of Justice to impose a fine of at least €46.5 million (£40m) for poor wastewater collection and treatment in Spain.
It has referred the country to the court again for not adequately collecting and treating urban wastewater discharged by 17 towns and cities.
In 2011, the court ruled Spain had breached EU law regarding the issue in 37 areas.
According to the Commission, it is still violating the regulations in 17 towns and cities, including Alhaurín el Grande, Isla Cristina, Tarifa and Coín. Around 1.4 million people live in the affected areas.
The Commission is also urging the court to impose a daily fine of €171,217.20 (£147k) if full compliance is not achieved by the date a second ruling is issued.