PARIS - France's Labour Minister joined the political opposition to a takeover of French retailer Carrefour by Canadian convenience-store operator Alimentation Couche-Tard, sending shares in Carrefour down 7% on Thursday.

Alimentation Couche-Tard's near $20 billion takeover approach for Carrefour - continental Europe's largest retailer - prompted the French government to raise concerns about national food sovereignty and job security at one of the country's largest employers.

"I am in favour of not questioning Carrefour's current shareholding structure and allowing (the company) to pursue its strategy, so (I am) opposed to a takeover," Labour Minister Elisabeth Borne told Europe 1 radio.

Finance Minister Bruno Le Maire on Wednesday had said he was not in favour of the deal at first glance.

Couche-Tard has made a non-binding 20 euros per share offer for the French grocery group, largely in cash. The Quebec-based company has given no further detail on its plans for the combined companies.

A source familiar with the discussions told Reuters that 20 euros per share was not enough but was a starting point for discussions.

The initial contacts between the two companies happened at the end of last year and Couche-Tard sent the first letter in early January, the source also said.

Shares in Carrefour were down 7.13% at 0851 GMT, after a 17% jump on Wednesday following the Couche-Tard approach.

(Reporting by Matthieu Protard; editing by John Stonestreet and Jane Merriman) ((matthieu.protard@thomsonreuters.com; +33-1-49495381;))