The European Union's competition watchdog has set a one-month deadline for Estonia and Poland to provide long-overdue information about their tax practices or face court action.

The EU's executive Commission asked all 28 member states last December to give details on tax rulings to establish if the procedures constitute state aid, but Estonia and Poland refuse to respond in full.

The EU's competition commissioner, Margrethe Vestager said Monday that "there are pieces missing. To have a complete overview we also need full information from Estonia and Poland."

The Commission opened tax probes last year into Apple in Ireland, Starbucks in the Netherlands and Amazon in Luxembourg.

The action against Estonia and Poland is part of its effort to crack down on sweet tax deals for multinational companies.