(Bloomberg) -- Spanish Prime Minister Pedro Sanchez’s coalition faces the worst threat to its unity so far, after its junior partner voted against changing a law that unintendedly lowered hundreds of sentences for sex offenders.

The opposition by far-left party Unidas Podemos to changes pushed by its Socialist partners to a law on sexual consent underscores deep divisions in the coalition. The tensions could hurt both parties in a key election year set to decide Sanchez’s fate.   

The main right-wing opposition party helped Sanchez push through his changes in an initial parliamentary vote Tuesday to close a loophole in the legislation, which has led to reductions of more than 700 sentences and the early release of 74 sex offenders, according to the judiciary’s governing body. The legislation, known as the “only yes means yes” law, states that sex without clearly expressed consent can be considered a sexual crime.

The clash could pave the way for a split in the coalition as both parties seek to shore up support ahead of a regional vote on May 28 and general elections by the end of the year. Sanchez, who is widely expected to run in the general vote, has said he intends to keep the alliance together until the end of his term later this year.

The proposal had 231 in favor, 56 against and 58 abstentions. The Socialists and the main opposition group, the conservative PP, both backed the proposal. 

‘Serious Rift’

“The disagreement over the law represents the most serious rift between PSOE and Unidas Podemos since the formation of the government,” Antonio Barrroso, of political consultancy Teneo, said in a note. Even if the coalition survives the dispute, “Podemos might eventually opt to leave the government if it believes it can recover some momentum in the opinion polls ahead of the legislative elections.”

Approved in August, the legislation, sponsored by Podemos, widened the definition of sexual assault and reduced the minimum length of prison sentences, which lawyers have used to obtain lower jail terms on appeal. The law aimed for assault victims to avoid having to prove they were subjected to violence or threats, by making consent a key element.

The Socialists introduced a clause last month to raise the minimum jail term for sexual aggression to six years if the crime involves violence or intimidation. Podemos says this weakens the law and puts the burden of proof back on victims.

While Sanchez is trailing the conservative Popular Party by at least two percentage points in opinion polls, he may still be able to stay in office if he reaches a deal with Podemos and other smaller regional parties to muster the 176 parliamentary seats needed to form a majority.

(Updates with votes in fifth paragraph.)

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