Spanish lawmakers have overwhelmingly approved a constitutional amendment to force the government to keep future deficits very low in a move to head off a bailout.

The Senate voted 233-3 in favor, brushing off opposition by leftist parties that abstained and labor unions that held protests in opposition to the amendment sought by investors to maintain confidence in the eurozone's fourth largest economy.

The vote Wednesday night means that the amendment is almost certainly headed for approval. Spain's lower house had already approved the measure proposed by Prime Minister Jose Luis Rodriguez Zapatero.

It appears unlikely that opponents will get enough votes from lawmakers to force a national referendum on the amendment.