A picture posted to Twitter by Northwestern law professor Eugene Kontorovich purportedly showing a French Michelin store in Turkish-occupied northern Cyprus. Photo: Twitter Screenshot.

A law professor at Northwestern University called out the French ambassador to the United States over a comment he made about it being illegal to do business with Israel because of the Jewish settlements in the West Bank.

Expert in international law Eugene Kontorovich took to Twitter, where French Ambassador to the U.S. Gerard Araud’s message was posted, and engaged in a back and forth before being blocked by Araud.

The issue erupted following incendiary remarks made by the CEO of French mobile giant Orange claiming his company was looking for a quick end to its contract with an Israeli partner operating domestically under the Orange brand. CEO Stephan Richard’s comment, which seemed to indicate that Orange’s lucrative contracts in the Arab world were at risk over its business in Israel, triggered a backlash among many Jews and Israelis who are increasingly alarmed by an apparently growing anti-Israel boycott movement.

Following Richard’s announcement, the French ambassador, himself a prolific Twitter user, posted the following message: “4th Geneva convention : settlement policy in occupied territories is illegal. It is illegal to contribute to it in any way.”

The Northwestern law professor, who also sits on the Jewish National Fund’s speakers list and blogs for the Washington Post, sharply rebuffed Araud’s message, saying no such legal precedent existed, either in France or in the international community.

Kontorovich mentioned the case of French multinational company Alstom, which a French court ruled did not violate international law by building in parts of the West Bank.

He mentioned Total, a French oil company with operations in the Western Sahara, to which the French ambassador replied, “There is oil in Western Sahara?”

The Northwestern law professor also posted a picture of a French tire-manufacturer Michelin, apparently from disputed territories in Northern Cyprus.

Eventually Kontorovich wrote in a piece for The Washington Post that the French ambassador blocked the law professor.

On Friday, Araud posted that “France condemns all boycott [sic] of Israel.”