Former Opposition leader Adrian Delia has urged President George Vella to refuse to sign into law the bill which would allow the termination of pregnancies when the mother's health is at risk.
The bill, he argued, does not respect the principles of the constitution on the right to life, and the president is the custodian of the constitution.
Times of Malta reported on Wednesday that the president had told close associates that he was considering resignation over the current bill, which is seen by various quarters as opening the door to abortion.
Vella had previously declared on several occasions that he would never sign a law allowing abortion.
The president's signature is the final stage of the legislative process and no law can come into force without it. The president's refusal to sign a bill approved by the democratically elected parliament has never happened in Malta and it would create a constitutional crisis.
The constitution actually does not give the president much of a choice, since it lays down that: "when a bill is presented to the president for assent, he shall without delay signify that he assents".
However, the constitution also says that a bill shall not become law unless it has been duly passed and assented to "in accordance with this constitution".
The president cannot be removed unless a motion for his removal is supported by at least two-thirds of the Members of the House.
Adrian Delia was leader of the opposition when Vella was nominated to become president three years ago.
In a letter to the president on Thursday, Delia said that Vella's declaration that he would not sign an abortion law was one of the reasons why the opposition had agreed to his appointment.
"You hold the office with the support of all the House, not a section of it, you represent all MPs, not some of them. You are the custodian of the constitution, not parts of it," Delia wrote.
"Every law must conform to the constitution, which protects the right to life and does not allow anyone to end it.
"You swore your loyalty to all the people and the Constitution in its entirety, not to the government," Delia wrote.
"I, therefore, urge you, as a person and a doctor who swore to protect life, as well as president and custodian of the constitution to hold firm, without fear, and not to abdicate your noble responsibilities,"
"Stand by the people and act according to your conscience and beliefs, which reflect the principles of the Constitution. Do not allow yourself to be an accomplice by absence, and do us proud. This is a moment of truth. It is a moment of choice and not the time to flee. Giving in now would lose us our soul," Delia said.
Delia signed in his personal capacity and he said when questioned by Times of Malta that it was not necessarily the position adopted by the Nationalist Party.
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