Liverpool and Tottenham supporters' groups have called on Champions League sponsors to return tickets so more fans can attend the final on 1 June.
The Premier League clubs have been allocated 33,286 of the 68,000 tickets for the Madrid final.
Spirit of Shankly and Tottenham Hotspur Supporters' Trust called on eight major sponsors to "redress the balance".
The groups said the move would "lift the occasion by increasing the number of passionate fans inside the stadium".
BBC Sport has contacted the eight companies named in a joint statement issued by Spirit of Shankly and Tottenham Hotspur Supporters' Trust - Nissan, Playstation, Gazprom, PepsiCo, Banco Santander, Mastercard, Heineken and Expedia Group.
Mastercard said sponsorship gives the company "access to exclusive opportunities to share with fans", such as being a Champions League mascot or attending fixtures during the season and including the final.
"Given the proximity to the final, all our and our partner promotions and offers have now closed, with tickets allocated," Mastercard said.
The other seven sponsors are yet to respond.
In March, Uefa's website said the two finalists would receive 17,000 tickets each, while 4,000 would be sold to fans worldwide via the Uefa website.
The remaining 30,000 seats at the Wanda Metropolitano Stadium would go to the local organising committee, Uefa, national associations, commercial partners, broadcasters and to corporate hospitality packages.
SOS and THST said their ticket allocations will mean many fans miss out on attending the showpiece final. The groups called on sponsors to lobby Uefa to allocate tickets more fairly and have already asked their clubs to subsidise the cost of tickets.
Liverpool held a ballot to determine fans entitled to the remainder of their tickets on Thursday, with thousands missing out and left on a waiting list.
Tickets have since appeared on resale website Stubhub priced from 3,450 Euros (£3,012).
Arsenal request Uefa explanation
Frustrations over the number of tickets allocated to the Premier League clubs for the Champions League final have been replicated by fans of Arsenal and Chelsea, who meet in the Europa League final on 29 May.
The London clubs will share just 12,000 of 68,700 seats at the Olympic Stadium in Baku, Azerbaijan.
Uefa have said the number of tickets issued was influenced by the difficulties fans will face in reaching Baku, despite the fact European football's governing body chose the host city over Seville and Istanbul in 2017.
On Thursday, Arsenal issued a statement expressing the club was "bitterly disappointed" with the allocation and called on Uefa to explain it's criteria for choosing venues.
"Time will tell if it is even possible for 6,000 Arsenal fans to attend the match, given how extreme the travel challenges are," the club said.
"On behalf of our fans, we would like to understand the criteria by which venues are selected for finals, and also how supporter requirements are taken into account as part of this.
"We have 45,000 season-ticket holders and for so many fans to miss out due to Uefa selecting a final venue with such limited transport provision is quite simply not right. The reality is that whoever reached the final would not be able to meet demand from their supporters."
In February, Uefa said 37,500 tickets would be sold to fans worldwide via their website, excluding those later offered to the two clubs reaching the final.
The rest will, as with the Champions League final, go to the local organising committee, national associations, commercial partners and broadcasters, and to corporate hospitality packages.