Despite voting in favor of ratifying the European Union constitution, Spanish lawmakers Thursday raised questions about what might happen if French voters reject the treaty in a May 29 referendum.

Mariano Rajoy, head of the opposition conservative Popular Party, said if the French 'no' campaign wins, as the latest polls predict, it could require drafting a new treaty, after Spanish voters approved the original charter in a ballot in February.

"Are you going to submit it to a referendum and tell the Spanish people that what they voted for is worthless because France says it is and you are going to subject them to a new treaty?" Rajoy asked his rival, Socialist Prime Minister Jose Luis Rodriguez Zapatero, in parliament.

Zapatero responded that the question was "totally premature" and advised not thinking about a Plan B.

"What everyone is doing is working for a 'yes,' and not allowing the possibility of a 'no,' or the consequences of a 'no,' or even the consequences of the consequences," Zapatero said.

After being approved by 311 Spanish deputies, the treaty now goes to Spain's upper house of parliament, the Senate, in about two months and if it passes as expected without amendments, the ratification will then take effect.

Spain was the first EU state to give the treaty popular backing in a referendum on February 20.

French voters will be the next to have their say in a referendum next month. Since mid-March, nearly two dozen surveys have indicated that a majority of French voters will reject the proposed constitution, with opposition hovering between 51 and 58 percent.