England goalkeeper Ellie Roebuck says the situation at Birmingham City is “unacceptable” following player complaints about conditions.
The letter, which has been seen by the BBC, addresses the differences of provision for the women’s team and the men’s at the club.
The BBC understands the Football Association plans to investigate.
“Looking in from the outside, it’s not good enough,” Roebuck said.
The Manchester City player added: “In the women’s game, we’re now at a level where that is not acceptable at all. I’m really lucky to be at a club where everything is top level and the equality throughout the building is top drawer.
“We all need to be at a level which can help players perform to the best of their ability. If they can be provided with better facilities, that will help the growth of the game and individuals. Hopefully it gets resolved.”
Birmingham City manager Carla Ward is acting as conduit between club and players following the complaints made by the team, which include access to the training-ground gym, changing rooms and travel to away fixtures.
The FA is also working with the women’s club and supporting them to ensure they are able to complete their remaining fixtures this season.
Other issues which the team have raised include lack of payments for non-contract players and others earning “less than the minimum wage”, delays over treatment for injured players and claims of an inadequate squad size. The letter says players had been compelled to play when not fully fit.
Roebuck’s England team-mate Lotte Wubben-Moy said: “Without a doubt I empathise. I cannot comment as I’m not a Birmingham City player but I respect them for speaking out and I think it’s an important part of their development as a club that the [player’s] voices are heard.”
The Arsenal defender added: “One of the nicest things about women’s football is we come together, we stick together to progress the game and it’s important we continue to do that.
“It’s amazing that so many players have stood with them on this. It’s important we continue to make our voices heard.”
The BBC contacted Birmingham City, who declined to comment.
However, in a statement given to the Telegraphexternal-link, the club said: “It’s no secret we have one of the lowest budgets in the league. Covid has only compounded this. This certainly makes it difficult to compete, but we’re doing our best on and off the pitch in what is a very difficult time for professional football.”
On travel arrangements, Birmingham said: “We are lucky to be based in the middle of the country where we can easily make journeys to our games without the need to stay overnight, whilst still being able to prepare our team in the best way possible to compete.”
In the letter, the players add: “The grievances laid out thus far have created a significantly unfavourable work environment. This prevents us from performing our jobs to the best of our ability.
“It has been significantly detrimental to the mental health of members of the women’s team.”
Birmingham have endured several setbacks this season. In January, they pulled out of a WSL fixture at Tottenham because of a shortage of available players due to injury.
The team also had some fixtures at their Damson Park home postponed this seasonexternal-link because of the poor condition of the surface. The letter claims the team do not have regular access to “suitable pitches”.
Birmingham are ninth in the Women’s Super League, three points above the relegation zone with four games remaining.
Several footballers have sent messages of support to Birmingham’s players.
Fran Kirby, the Chelsea and England forward, tweeted: “It’s a shame in 2021 we still have women’s teams competing in the top league in England having to ask for help like this. We should all be given the chance to perform at the highest level we can, Birmingham Women we all stand with you.”
Meanwhile, Kirby’s international team-mate Leah Williamson called it “another example of the imbalance between expectations of women’s athletes and the support provided to them”.
The Arsenal defender added: “Things have to change to help, not hinder them.”