Australia’s two-game series with the United States is in jeopardy after Matildas players went on strike in the latest move over Collective Bargaining Agreement negotiations.

Australia is scheduled to play the United States on Sept. 17 in Detroit and Sept. 20 in Birmingham, Ala., as part of the U.S.’ World Cup victory tour.

Football Federation Australia chief executive David Gallop says the USA-Australia games are now “looking very unlikely.” Reached by The Equalizer, a U.S. Soccer spokesman said: “We are aware of the situation and are in communication with Australia.”

The FFA said it condemned the Professional Footballers Australia’s decision. The PFA instructed the players to boycott practice, hours before negotiations on a Collective Bargaining Agreement were set to restart. Australia coach Alan Stajcic was forced to cancel practice on Tuesday due to the boycott.

The PFA wants an increased salary cap for each of the 10 A-League clubs. It wants an increase in payments for international matches and increased spending on wages, air travel, accommodations and benefits for the Matildas, who made it to the quarterfinals at the 2015 World Cup.

“It’s sad that the Matildas have been dragged into a dispute that’s primarily about the A-League,” the FFA said in a statement. “The offer to the Matildas would basically double their pay over the next four years.”

The FFA said it “opened the books” to show the PFA what it could afford, saying that the PFA’s demands are unrealistic.

“This was an extremely difficult decision to make,” Australia goalkeeper Lydia Williams said. “For the past two months the players have been unpaid and have made every attempt to reach an agreement that gives the women’s game a platform for growth.

“This is about the future of Australian football. We want to establish football as the sport of choice for Australian women, and we want to be one of the best nations in the world.”

Australia’s men’s team was instructed to boycott sponsored community events before a World Cup Asian qualifier in Perth last week.

“It’s sad that the Matildas have been dragged into a dispute that’s primarily about the A-League,” the FFA said in a statement. “The offer to the Matildas would basically double their pay over the next four years.”

We play together & we will stand together . #protecttheplayers — Sam Kerr (@samkerr1) September 8, 2015