Laporte and Toulon owner Mourad Boudjellal outlined the club's policy on Thursday in a meeting with Wales caretaker coach Rob Howley and the Lions boss Warren Gatland. Gatland was told that Toulon will not allow Jenkins to join up with Lions for the start of next summer's tour to Australia if they qualify for the Top 14 final on June 1.
That stance leaves Jenkins in danger of missing out on a third Lions tour because Gatland wants his whole squad to be together in Hong Kong for their opening match against the Barbarians, also on June 1.
The four-way conversation then turned to Wales and Toulon stated Jenkins would not be available to face the Wallabies in December because the match falls outside the official international window.
"The chat was very friendly," Laporte told L'Equipe. "We discussed the availability of Gethin Jenkins. We said again that we would not release him to leave with the Lions on May 27 if we are in the final. He understood. I think he already knew when he came to the meeting.
"We did not talk so much about the Lions. It was more about Gethin's availability for the November and the Six Nations. On December 1, the Welsh play a Test against Australia outside of the window and we told them that the position of principle was the same as for the Lions tour: 'No'. Toulon play Grenoble on the same day in the Top 14."
Jenkins knew the potential ramifications on his international career when he signed for Toulon last summer and it is understood he accepts it could cost him a place on the Lions tour.
The Welsh prop, who has started five of the Lions' last six Test matches on the 2005 and 2009 tours, does not have a release clause in his contract and so his loyalty in any tug-of-war would have to lie with Toulon.
"As far as freeing up Gethin (to fly out with the Lions if Toulon reach the Top 14 final), it's a no," Laporte said.
"You don't pay a player to be playing with the Lions at the most important moment of the season." Gatland and Howley will also be meeting Perpignan and Bayonne during their trip to France, to discuss the release of players like Mike Phillips, James Hook and Luke Charteris.