Tens of thousands of anti-government protesters took to the streets in Morocco's largest city, Casablanca.
The rally, organised by trade unions, was believed to be the biggest since a new government took office in January.
Those taking part accused Prime Minister Benkirane of failing to deliver promised reforms.
Morocco's King Mohammed VI managed to hold off Arab Spring protests last year by curbing his powers and pledging a raft of reforms.
In November, polls brought to power a coalition government led by the Justice and Development Party, a moderate Islamist party, but many are frustrated over the pace of change in a country plagued by high unemployment and illiteracy rates.
'United message'
"There are more than 50,000 people who are demonstrating to call on the government to start a genuine dialogue addressing our country's social ills," opposition Socialist MP Hassan Tariq said on Sunday.
"The trade unions are united and the message to the Benkirane government is clear: he needs to change his strategy," he told AFP news agency.
An official put the number of demonstrators at between 15,000 and 20,000, according to AFP news agency.
Trade unions have been calling for an improvement in salaries and social conditions in Morocco, where almost half of those aged between 15 and 29 are unemployed.
Last year, after the country found itself caught up in the protest movement that swept through the region, the king unveiled a new constitution and promised to transfer powers to an elected government.
Morocco's talk of a democratic agenda went down well internationally, but critics say the changes were largely cosmetic.