Public sector workers went on strike Thursday across France in a warning shot against President Emmanuel Macron's reform drive.

Protesters and police clashed on the first day of planned strikes in Paris, causing cancellations of trains and flights. The demonstrations are the latest test for the strength of the president as he tries to stick to his agenda of overhauling state rail operator SNCF and other public services. More than 140 protests have been planned across the nation. France's once-fearsome unions have regularly forced governments into policy U-turns in the past, but Macron and his ministers have vowed not to yield.