"We want this to act as a deterrant to future opponents who look to increase ticket prices for our travelling supporters", the United letter continued.
In the email, seen by Press Association Sport, United's head of ticketing and membership Sam Kelleher wrote: "In this instance we believe that our travelling supporters are unfairly being subjected to increased/excessive ticket prices from the host club".
Sevilla were accused of setting "exorbitant" prices when it emerged they would be charging United fans at least £89 for the game.
Sevilla are charging United supporters £89 for a ticket in the uncovered away end at the Estadio Ramón Sánchez Pizjuán.
Jose Mourinho's men face Sevilla in the last 16 of the Champions League and those who travel to the first leg at the Ramon Sanchez Pizjuan on February 21 will have to pay £89 as a visiting fan, £35 more than Liverpool supporters were charged at the same venue in December. The club will then use the €40 difference per ticket they stand to earn to subsidise their own fans travelling down to Sevilla for the return.More news: TCL Make Hisense Look Second Rate AT CES 2018
Sevilla claim that United have not followed UEFA's ticket guidelines in allocating 5% of the tickets to their supporters and had been given just under 3,000 tickets when they should have had 3,800.
Sevilla get round the regulations on ticket prices because they have also increased the prices home fans will need to pay to watch the game.
Any additional proceeds will be donated to the Manchester United Foundation.
A club source told Reuters: "Right now everything is hypothetical as United have not informed the club officially of the price rise".
United attempted to persuade Sevilla to lower their prices but discussions between the two clubs failed to lead to a significant reduction.
Sevilla refused to back down and so now Manchester United have chose to charge visiting Sevilla the exact same amount. "We are delighted United have fought our corner on this issue".