UPDATE 1-Riot police save France's Pinault from workers

* Billionaire Pinault blocked by protesters

* Managers at Caterpillar factory barricaded in office

* Labour relations in France increasingly tense

(Adds background, updates Caterpillar, Continental protests)

By Crispian Balmer

PARIS, March 31 (Reuters) - Angry shop workers facing the sack blocked French billionaire Francois-Henri Pinault in a taxi on Tuesday before riot police were called in to clear away the protesters, officials and police said.

Pinault, chief executive of retail and luxury group PPR (PRTP.PA), was surrounded in a car in central Paris by staff from two of his stores that have announced 1,200 job cuts.

"They briefly delayed Mr. Pinault's car as he was leaving a company meeting," said a spokesperson for the group.

French radio said he was blocked for an hour before the CRS riot police, brandishing shields, secured his release.