Witnesses say at least one person was wounded.
The police crackdown comes in the wake a Saudi ban on protests announced earlier this month. The government enacted the ban after several small groups of demonstrators gathered to demand change in the conservative kingdom.
Large opposition rallies are very unusual in Saudi Arabia, but several thousand people have joined Internet groups calling for Friday’s protest in the capital, Riyadh. Organizers say they will use the rally to call for major political and social change.
The incentives included pay raises, increased spending on social programs and interest-free loans.