The European Union has given Belgium until later today to end its opposition to the Comprehensive Economic and Trade Agreement (CETA) - a free trade deal with Canada.

The left-leaning Wallonia region of the country argues that the agreement is bad for EU farmers.

Its leader, socialist Paul Magnette, told local media that the ultimatum is "not compatible with the exercise of democratic rights".

Alik Keplicz AP/Press Association Images

"Difficulties remain, especially on a symbolic and extremely important politically issue: the settlement mechanism," he said late last week.

Mr Magnette highlighted difficulties surrounding the uncertainty regarding the issues of settlements between states and corporations:

"The mechanism is not described with precision ... It's like buying a cat in a bag," he told the the Walloon parliament.

Canada has warned EU leaders that the ball is now in their court to finalise the deal.

After years of negotiations, European Council president Donald Tusk will speak to Belgian prime minister Charles Michel later today according to Reuters. Canadian prime minister Justin Trudeau is due to fly to Brussels to sign the deal on Thursday - if the Belgian region holds-out this trip and an accompanying EU/Canada summit will be postponed, The Guardian reports.

"Regarding Thursday, if Belgium is not in a position to say that they guarantee they can sign, it’s very clear for Tusk that it doesn’t make sense to have a summit, and there will be no summit, and there will be no date set for a new summit," a source told the newspaper.

The Belgium government cannot agree to the deal without the consent of its five regional counsels, including Wallonia, a French-speaking region in the south.

The main concern expressed by opponents to the agreement is that the investment protection deal gives too much power to corporations.

CETA would reduce trade barriers between the EU and Canada, the world's tenth largest economy.