ATHENS – The fall-out over claims the brother and sister of Prime Minister Alexis Tsipras and Radical Left SYRIZA leader Alexis Tsipras won a 1.1-million euro ($1.29 million) state contract for their construction firm after submitting fake social security documents is still being pressed by the major rival New Democracy.

The Conservatives presented what they said were documents backing up their claims although it wasn’t reported what they were nor what they said.

The building firm, Diodos, managed by Tsipras’ brother Dimitris, got the award “in full knowledge” that the social security clearance certificate used to secure it was fake, New Democracy said.

Dimitris Tsipras had been indicted over the case in 2015 after his brother came to power but it was on misdemeanor instead of more serious criminal charges and the Conservatives said a SYRIZA amendment to the statute of limitations law prevented prosecution.

New Democracy leader Kyriakos Mitsotakis, who has taken his party to big leads in polls after Tsipras repeatedly reneged on anti-austerity promises, said his “non-negotiable political priority” was to defend the rule of law.

There was no explanation why the siblings of a Prime Minister were allowed to make a bid on state work. Dimitris Tsipras and his sister, Zanet, threatened to sue if New Democracy keeps up the barrage of questions over their contract.

“Because over the past few days ND is mudslinging and leaking vile charges against us, through its friendly press, we would like to emphasize that libel is a civil and criminal charge; it is not justified by any opposition fury, and will be dealt with by the courts, where every law-abiding citizen can seek recourse.”

Ironically, they raised the question of suing for libel at the same time Tsipras has claimed 10 rival politicians took bribes from the Swiss pharmaceutical company Novartis without providing any evidence beyond his accusations.

New Democracy spokeswoman Maria Spyraki earlier renewed the questions around the case. A claim was also made by the right-leaning Parapolitika paper, which claimed that Tsipras’ siblings company got a preferential treatment to settle a loan of 243,544 euros ($285,938) with 67 years to repay it.