Sarkozy broke a taboo last December when he emphasised France's Christian roots at a speech in Rome basilica, referring to France as "the eldest daughter of the Church" and stating that "the roots of France are essentially Christian".
Some say his speeches, including his latest in Saudi Arabia's capital city, ignore a French law separating church and state.
"A speech citing God not only on every page, but on every line, creates a fundamental problem for the republic," argued Socialist Jean Glavany at the National Assembly last Wednesday, referring to Sarkozy's speech earlier in the week on providing state subsidies for faith-based groups.
Last Monday, in Riyadh, Sarkozy hailed Islam as "one of the greatest and most beautiful civilisations the world has known" and described his Saudi hosts as rulers who "appeal to the basic values of Islam to combat the fundamentalism that negates them".
His praise for a kingdom that enforces and propagates a strict interpretation of Islam - during a visit aimed at securing lucrative export contracts - was the last straw for many of his critics.
"This is not respect for the separation of church and state," socialist opposition leader Francois Hollande said, according to Reuters.
"This is an ideological stand that makes religion into an instrument to promote French products civilian nuclear plants for Muslim countries," he said. "Mixing religion and foreign policy is illogical and wrong."
The head of the Constitutional Council, Jean-Louis Debre, indirectly chided Sarkozy by saying the 1905 law separating church and state was a good one and that it was "opportune to make sure its balance is not upset", Reuters reported.
Interior Minister Michele Alliot-Marie responded by saying the Frech Government wanted "to help all spiritualities to express themselves, including those based on atheism".
Although the 1905 law aimed at undercutting the vast influence the Roman Catholic Church once wielded in France, church leaders now are reserved about any reforms that could upset the status quo and revive anti-clerical movements.
The strict separation of church and state began with the enactment of law in 1905 that grew into a form of political correctness that made bringing religion into public affairs a major taboo.
Sarkozy has called this a negative "laicite" - the French term for church-state separation - and wants a "positive laicite" that values the hope that faith brings and allows state subsidies for faith-based groups.
The twice-divorced president defines himself as a "cultural Catholic" - an infrequent churchgoer who says he values the moral and social role that religion can play in society.
"Someone who believes is someone who hopes," Sarkozy said in the speech in Rome's Basilica of Saint John Lateran. "It is in the republic's interest to have many men and women who hope."
On a personal note, Sarkozy chose not to comment on the enquiry from press about his marriage with supermodel-turned-singer Carla Bruni.
"Stop, then, from being interested in my private life," he said.
In a report this past week, the regional daily L'Est Républicain alleged that Sarkozy and Bruni married earlier this month in a "small, private ceremony" at the Élysée presidential palace.