Spain's Prime Minister Pedro Sanchez pledged on Sunday to criminalise prostitution in the country.
Speaking to supporters at the end of his Socialist Party's three-day congress in Valencia, Mr Sanchez said that the practice "enslaves" women.
Prostitution was decriminalised in Spain in 1995 and in 2016 the UN estimated the country's sex industry was worth €3.7bn (£3.1bn, $4.2bn).
A 2009 survey found that up to 1 in 3 Spanish men had paid for sex.
However, another report published in 2009 suggested that the figure may be as high as 39% and a 2011 UN study cited Spain as the third biggest centre for prostitution in the world, behind Thailand and Puerto Rico.
Prostitution is currently unregulated in Spain, and there is no punishment for those who offer paid sexual services of their own will as long as it does not take place in public spaces. However, pimping or acting as a proxy between a sex worker and a potential client is illegal.