FFA chief executive David Gallop has called the PFA's demands for more money unreasonable. Morne de Klerk/Getty Images

Football Federation Australia (FFA) chief executive David Gallop has warned that the ongoing feud between Professional Footballers Australia (PFA) and the governing body may impact the start of the 2015-16 A-League season.

In response to Tuesday's unprecedented action which saw the Australian women's national team, the Matildas, withdraw from a scheduled training camp ahead of a tour to play world champions the United States, Gallop told the ABC that he could not be "100 percent confident" that Australia's football season would kick-off on time.

The impasse in negotiations between the FFA and PFA appears to be centred around the PFA's new demands for an extra $3 million in salary payments for A-League players over the next two years, and a significant increase of investment in women's football -- both measures that the FFA argues are not practical.

"We've invested a lot in their program in the last year to prepare [the Matildas] for Canada and the World Cup," Gallop said.

"Now we've provided an opportunity for them to play the world champions, 60,000 tickets have been sold.

"Yes we would love to pay them more but unannounced, fresh demands yesterday is no way to go about it."

The Matildas' upcoming tour of the United States is now in serious doubt. no_source

Earlier in the day, all ten Australian A-League clubs threw their support behind the FFA in the ongoing feud in a joint statement.

"The PFA has shown its reckless regard for the clubs who collectively employ over 200 professional players," Adelaide United FC Chairman Greg Griffin said.

"The demand for another $3 million in payments is a dangerous folly, especially in such a young league. Do they want to send clubs broke before they comprehend the damage?

"We keep hearing from the PFA about respect for players. What about respect for clubs, their staff, members and sponsors? Respect is a two way street.

"In any negotiation all parties must treat each other with respect. Whilst I completely disagree with what happened yesterday I respect the right of the players to negotiate as hard as they deem required.

"However, to seek to introduce at this late stage game-changing demands that the PFA knows the game cannot afford and the Clubs will not agree to, is to disrespect the process that has been ongoing for seven months.

"I urge the PFA to return to the table and conclude these difficult negotiations in good faith without stating demands which they know will be rejected and which only purpose appears to be to antagonise the FFA and the Clubs."

Sydney FC Chairman Scott Barlow echoed Griffin's sentiments, saying: "The PFA has lost all sense of perspective with this latest round of demands. Their new claims are unaffordable and plainly irresponsible.

"The PFA needs to realise we must have financially viable clubs if the A-League is going to grow and achieve its potential.

"Today the majority of A-League clubs are still losing money and the PFA's latest demands would simply push clubs further into debt. We cannot afford to see clubs go broke.

"Financial security for players will only be achieved when clubs are financially stable."