AP

Even actor Tom Hanks has an opinion about whether the athletes at the 2015 Women's World Cup should play on artificial turf or grass.

A group of players from the U.S. women's national team, who will vie for a spot in the World Cup in October qualifying, have joined with several international players in protesting the turf surfaces for next summer's big event in Canada. And they're getting rapidly growing support from the sport's fans, including Hanks.

Last week Hanks, a big soccer fan, voiced his support on Twitter: "Opinion: Women's World Cup is the best Soccer of the year. Hey FIFA, they deserve real grass. Put in sod. Hanx."

The athletes say that it's not just a safety issue because turf is less forgiving than natural grass, it's about equity. They argue the men weren't asked to play soccer's top international tournament on a fake surface.

"It really goes down to this: The men would never play a World Cup on turf, so why should the women? It's the same tournament. It's the World Cup," U.S. forward Sydney Leroux said. "It's the biggest thing that we have for soccer. Why would we play on something that's not real?"

The athletes have formally joined in a letter of protest penned to FIFA, the sport's international governing body, and the Canadian Soccer Association. If they don't hear back soon, legal action could be taken in Canada based on that country's laws against gender-based discrimination.

Boies, Schiller & Flexner, the law firm involved in the recent lawsuit filed by former UCLA basketball star Ed O'Bannon against the NCAA, drafted the letter on behalf of the players and is prepared to go to court.

"I think it resonates with a lot of people," said Boise Schiller & Flexner attorney Hampton Dellinger. "It's important in and of itself, but it's also important on a symbolic level, that if some of the world's greatest athletes can be treated this way, it's a real setback for gender equity in sports. It should have never gotten to this point, but it's not too late for Canadian soccer and FIFA to do the right thing."

In an email to The Associated Press, FIFA acknowledged receipt of the letter, but declined further comment. The Canadian Soccer Association deferred to FIFA for reaction.

But Victor Montagliani, president of the Canadian federation and chairman of the national organizing committee for the World Cup, addressed the issue during a press conference in advance of the FIFA U-20 Women's World Cup final last Sunday in Montreal.

"I know players in other tournaments with natural grass have complained about the quality of the surfaces there. That's the nature of players. The truth is that our bid went in according to FIFA regulations, and we're focusing only on this current tournament and next year," Montagliani said.

FIFA changed its rules in 2004 to allow sanctioned matches on certain artificial surfaces. A few games at the 2010 men's World Cup in South Africa were played on grass that had been reinforced by artificial fibers.

Canada's bid stipulated that the final be played at Vancouver's BC Place, which seats 55,000 and has an artificial turf. The games will be played in six stadiums across Canada, in some places where growing and maintaining natural grass is at times tricky. FIFA regulations state that all matches and practices be held on the same surface.

But the dispute is generating buzz after NBA stars Kobe Bryant and Kevin Durant went to Twitter in support of the players.

Bryant tweeted a photo of Leroux's battered legs after playing on turf.

"It's crazy. Should be grass stains, not blood," Leroux said. "How are you supposed to play with raspberries all over your legs in two, three days. You can't play as hard."

Some suggest the players are more timid on artificial turf and the game itself is impacted.

"It's a really big difference. The ball slides on turf. The bounce is different. Everything is different. It's not as real as grass. You can't slide tackle someone, you can't do all the great things that come with playing soccer, on turf, you just can't," Leroux said.

U.S. midfielder Megan Rapinoe lamented: "It's basically playing on padded concrete."

The controversy is not new. Many players were voicing their concern even last summer, when the U.S. team played a friendly in Canada. Striker Abby Wambach called out FIFA for gender discrimination and started a petition, which led to the letter sent to FIFA and the Canadian Soccer Association in late July.

"The best players in the world deserve premier playing surfaces. Simply put, artificial turf is not a premier surface in the soccer world," the letter states.

The United States is hosting the CONCACAF qualifying tournament for the World Cup in October. All of the fields to be used in the tournament are natural grass, despite the weather.

Many players believe that FIFA and the Canadian federation could cover the six fields that will be used for the World Cup with sod. The real stuff was rolled onto the artificial surface at Michigan's Big House this summer for a match between Manchester United and Real Madrid.

It's not ideal, they say, but better than the alternative.

"Is it going to cost them a little bit of money? Yeah. Maybe a drop in the bucket for FIFA for the amount of money that they have," Rapinoe said. "It just seems like they're kind of like, 'Oh, yeah, whatever, this is just what you're going to have.' When there's an alternative option, that's frustrating."