A top Turkish court on Thursday suspended funding for the main pro-Kurdish party ahead of its possible ban over alleged terrorism ties.
The constitutional court decision deprives the Peoples' Democratic Party (HDP) -- parliament's second-largest opposition group -- of a key source of income heading into a general election due by June.
President Recep Tayyip Erdogan accuses the party of being the political wing of banned militants who have been waging a decades-long insurgency against the Turkish state.
The HDP denies formal links to the fighters and accuses the government of targeting the party because of its strong opposition to Erdogan.
Thousands of supporters and dozens of its current and former officials currently languish in jail on highly contentious charges that have strained Turkey's relations with leading main allies in the West.
The party compared Thursday's court ruling to an illegal seizure of assets and vowed to win in the polls.
"This decision, which aims to prevent a fair and democratic election process and to ignore the will of the voters, neither prevents our loss of power nor our greater victory," it said a statement.
Emma Sinclair-Webb of Human Rights Watch of said the decision offered more proof "that Erdogan's government uses courts to disadvantage, remove and punish the political opposition".
- Possible ban -
The HDP's future could play a major role in deciding Erdogan's success in parliamentary and presidential elections that pose one of the stiffest challenges of his two-decade rule.
Turkey's constitutional court is hearing a prosecutor's request to ban the party before the vote.
Chief prosecutor Bekir Sahin is due to argue his case in court on Tuesday.
The court will then have the option of either dissolving the party or banning some of its members if it rules against the HDP.
Turkish media reports say the party was due to receive 539 million liras ($29 million) in treasury funding this year.
The party holds 56 of parliament's 579 seats and usually votes together with other opposition parties.
An HDP party spokesman told AFP that the party's only other source of revenue is supporter donations.
The spokesman could not immediately say what percentage of the party's funding comes from the state.
Thursday's ruling came less than a month after another court banned Istanbul's popular opposition mayor Ekrem Imamoglu from politics.
Imamoglu has emerged as one of the more likely opposition figures to beat Erdogan in a head-to-head race.
The mayor will hold on to his job while the ruling is appealed.
But he would have to resign if he were elected and his political ban was upheld.