Manchester United supporters have asked the club to improve the atmosphere at Old Trafford.
The letter, addressed to group managing director Richard Arnold, says "expansion [of Old Trafford] is essential to fully address the key issues" but also outlines "interim measures" that can be put in place more quickly.
Fans have asked for the executive seats in the Stretford End to be removed along with relocating the Family Stand.
The letter reads: "As you know the atmosphere in the stadium is a key issue for supporters and also for the manager and the team.
"We are keen to push ahead as quickly as possible on discussion of interim measures which will produce progress while we await the major stadium development that is so badly needed.
"While we understand that the issue of stadium expansion at Old Trafford remains under active consideration, and that a firm decision has not yet been made on whether the investment will be made into a significant capacity increase, we recognise the major financial, technological and logistical challenges this presents.
"For that reason, in this letter, we intend to concentrate primarily on interim measures which could be taken to improve atmosphere and develop the stadium in the absence of expansion."
Jose Mourinho has been critical of Old Trafford's atmosphere since taking over in 2016.