Ground staff at Rio de Janeiro's airports plan to stage a 24-hour partial strike on Thursday, the day Brazil hosts the opening match of the football World Cup.

The workers pledged to maintain 80 percent service, but the strike will raise fears of delays as thousands of football fans descend on the city around the opening match in Sao Paulo and the first game in Rio on Sunday.

The walkout, which takes effect from midnight on Wednesday, will affect Rio's Galeao international airport, and the Santos Dumon airport, which provides domestic services to Sao Paulo.

Al Jazeera has been unable to confirm if the city's Jacarepagua airport will also be affected.

Sao Paulo, which hosts Thursday's opening match between Brazil and Croatia, is a 40-minute flight from Rio.

The umbrella union that represents the workers is calling for World Cup bonuses, better working conditions and raises of up to 12 percent, but says employers are offering a maximum of eight percent.

"After nine months of intense but failed negotiations and intransigence from employers, the Rio de Janeiro Municipal Airports Employees' Union confirms it will strike on June 12," the union said on its website.

Court injunction

More than three million Brazilians and 600,000 foreigners are expected to travel in Brazil during the tournament, which wraps up with the final match in Rio on July 13.

A labour court has issued an injunction ordering the unions to maintain staffing at 80 percent of normal levels or face fines of up to $22,400.

Meanwhile, subway workers in Sao Paulo voted on Wednesday against resuming a five-day strike that would have caused traffic chaos during the opening game.

The workers went on strike last week, but suspended their action on Monday night for two days to decide whether to walk out again during Thursday's Brazil-Croatia match.

Sao Paulo riot police firing tear gas had clashed with the striking subway workers who had continued to stay away from work despite a court declaring their strike to be illegal.