The massive protests planned by the opposition over Nigeria's disputed elections have failed to materialise.
Opposition leader Muhammadu Buhari is expected to join the rallies
They had hoped to use the trade unions' May Day rallies to denounce what they see as election fraud but the rallies went ahead as usual.
The police deployed across the country warning that unauthorised demostrations would be forcibly broken up.
A BBC correspondent in Lagos says few people seem willing to put their lives on the line for elitist politicians.
"We don't want to use today to state any sort of grievances by anybody," one union official said.
"That would then turn into people being molested, or all sorts - yes we may have our reservations about the elections or whatever, but today's our happy day and we don't want it to be jeopardised."
Local election observers have condemned the presidential, legislative and state polls as a "charade", with results declared in areas where no voting took place.
The ruling People's Democratic Party's Umaru Yar'Adua was declared the winner of the 21 April presidential election, with 70% of votes cast.
The BBC's Alex Last says the fact that the unions were rather reluctant to have their events used for political means highlights the lack of unity amongst those who have condemned the election.
As the elections slowly move into the distance and millions of Nigerians contend with their daily struggle for survival, it will only get harder to build the momentum to force a change, he says.
Security was tight at the Lagos rally - busloads of police were outside the stadium, inside union officials were in control.
"I think people seem to be cowed by the intimidation of the security agencies, because we witness that here a lot," an activist said.
Police chief Sunday Ehindero said May Day rallies were allowed at designated grounds, but police would crack down on those marching without a permit.
The police have warned against unauthorised marches
"Any procession that takes place without a police permit will be dispersed forcefully, it will be tear-gassed and if greater force is required, we will use it," he warned.
On Monday, top election observer Emma Ezeazu was arrested by state security officials, who accuse him of inciting violence.
The agents from the State Security Service (SSS) raided the Alliance for Credible Elections (ACE) office and confiscated placards being readied for the protests, ACE says.
"They said they didn't need a warrant to arrest him," ACE spokesman Odoh Okenyodo told the BBC's News website.
"They said they caught us in the act of producing placards for tomorrow's mass protests.
"But this will not break our will. International and local observers all agree that the recent general elections in Nigeria were terribly rigged.
"We were only preparing those placards to join in the peaceful protests called tomorrow by the central labour union" he says.
Mr Ezeazu witnessed several irregularities during the polls.
"People were forced to thumb-print in front of the PDP agents and then they took the ballot and put it in the ballot box," he told the BBC.
Some 200 people were killed in election violence, according to European Union observers.
Our correspondent says the opposition has been reluctant to call for street protests because it fears they could spiral out of control.
Opposition parties have called for the annulment of the elections.
But the government has rejected criticism of the elections, saying it was intended to cause a coup.
President Olusegun Obasanjo is due to hand over power on 29 May, in what should be the first transition from one civilian leader to another in Africa's most populous nation.