The Spanish Student Union finds the poster "insulting"
With less than a month to go before Spain holds the EU's first referendum on the European Constitution, not everyone is happy with the campaign.
A row has erupted over an advert for Referendum Plus - a canned drink.
It is being handed out to people under 34 with the claim that it can inspire them to turn out on 20 February.
The poster, put out by the government-funded Youth Council, shows a monkey turning into a voter after downing the contents of the can.
Referendum Plus, it claims, will end the apathy that has long dogged European elections.
"This drink could change your life," reads the caption. "Thanks to its stimulating action against fatigue, you'll go out and vote."
There is also a quote from a fan rating it above calimocho, a mixture of wine and cola popular among young revellers.
But the Spanish Students' Union has demanded the poster be withdrawn.
December 2004 poll on Spanish EU Constitution awareness
84% don't know what's in the European Constitution
55% believe it will be good for Spain
50% believe it will benefit the autonomous regions
Support for "yes" - down at 42%
Support for "no" / undecided / won't say - up at 38%
"Turnout must be encouraged through arguments and patience, never through divisive messages insulting young people who don't vote," says the union, according to El Mundo daily.
The Youth Council's president, Lucia Sala, disagrees.
"It's about raising young people's awareness that voting is a big responsibility that allows us to criticise those who govern us," she said.
Nor is this the only bone of contention in the referendum campaign. Its key slogan - "The first in Europe" - was rejected after an appeal by Catalan leftists.
The Central Electoral Board ordered that "value judgments... which may, directly or indirectly, influence citizens' positions or attitudes" must be removed.
The slogan had to be changed, but this failed to placate the United Left (IU), a coalition led by the Spanish Communist Party.
IU leader Gaspar Llamazares questions what he sees as the surrender of national sovereignty to Brussels. And, he says, the EU Constitution promotes market forces over workers' rights.
Socialist Prime Minister Jose Luis Rodriguez Zapatero, however, insists on the virtues of the document.
"When, on 20 February, citizens can go to the ballot boxes and pick up their ballot papers, they will have there a weapon of mass construction," he said on Spanish TV.
BBC Monitoring selects and translates news from radio, television, press, news agencies and the Internet from 150 countries in more than 70 languages. It is based in Caversham, UK, and has several bureaux abroad.