French job law 'constitutional'
Students and trade unions have called for another one-day strike next Tuesday in a drive to get the law scrapped.
If the Constitutional Council rules the law valid, it could be put into effect at once by President Jacques Chirac.
The president is expected to address the nation soon – possibly as early as Thursday evening, correspondents say.
Universities across the country have been disrupted for weeks by protests over the First Employment Contract (CPE), which would make it easier for employers to fire workers aged under 26.