I think the government will not interfere about of transferring players, even though it is a source of state/city government revenue, because of the player's tax payments. players have the exclusive right to determine their future at a club. The clause to end his career in Barcelona next season is a decision by the player, the Spanish government and the Spanish football organization also have no right to prohibit Messi from deciding this.
according to his interview with catalan radio a year ago, he said that he considered leaving Barcelona after the tax problem.
it's like he wants to leave spain, but not Barcelona (at that moment).
he was the first top player to be targeted by spanish tax authorities.
spanish tax authorities might not explicitly interfere the current situation between Barcelona and messi.
but they can implicitly do something like being "soft" to messi with his tax
. 
