Mariano Rajoy Reuters

Spain’s Prime Minister Mariano Rajoy is facing renewed pressure to resign after more damning evidence was revealed that linked him to former Popular Party Treasurer Luis Barcenas, who is on trial for corruption and tax fraud.

Spanish newspaper El Mundo reported that Rajoy sent Barcensas text messages of support as he awaited a trial that threatens to destabilize the current Spanish government.

El Mundo reported that the message from Rajoy was from January, around the time the allegations broke.

He said: "Luis, I understand. Stay strong. I'll call you tomorrow. A hug."

Barcenas is due to appear in court on Monday, just one week after he admitted that his handwriting was on a document that outlined payments that had been paid to him and other party leaders. It is alleged that he stashed up to $55 million of party donations and illegal kickbacks in a Swiss bank account.

Opposition party leader, Alfredo Perez Rubalcaba of the Socialist Party, has called for Rajoy’s immediate resignation.

"Mr. Rajoy's conduct in this situation can be summarized quite simply: silence, lies and after what we have learned today, collusion, extremely serious collusion," Rubalcaba said.

In June, a judge ordered that Barcenas remain in jail until the beginning of his trial as he was considered a flight risk.

Both Rajoy and Barcenas deny any wrongdoing.