The Segunda Division B side's squad has given the club's president an ultimatum as he has been unable to resolve their precarious financial situation
The players of the Segunda Division B side have released an official statement to announce they will not show up for the second leg of the quarter-final tie unless Lavin resigns from his position out of protest over unpaid wages.
"Despite promises that the situation would be resolved, the board still owes the players several months of wages," the statement reads.
"The refusal to sort this situation has led to financial problems for several squad members. Therefore, the squad demands the immediate resignation of the president.
"If the president refuses to step down, we will not play the return of the Copa del Rey match against Sociedad."
Santander were beaten 3-1 by Sociedad in the first leg of the quarter-final tie.
The Sardinero side were still playing in La Liga in 2011-12, but they have dropped to the third tier following two consecutive relegations due to their financial difficulties.