Economy Minister Luis de Guindos has threatened to introduce means-tested health care — but his comments were disowned within hours by the ruling Popular Party.
Mr Guindos attempted on Monday to portray abolishing universal free health care as progressive, arguing that those who earned over €100,000 (£83,000) ought not to rely on "the taxpayer" for health services.
But the comments sparked fears of a slippery slope in a country where health care is provided by regions rather than the central government.
Catalonia has already undermined the free service by introducing co-payment for prescriptions.