Just three days ahead of Zimbabwe's presidential election, President Robert Mugabe today gazetted new electoral rules the opposition claims gives him an unfair advantage in the hotly-contested poll.
The legislation added to increasing confusion over how and where voting will take place on Saturday and Sunday.
The opposition Movement for Democratic Change (MDC) said it would not allow President Mugabe's move to go unchallenged.
"We find it completely unacceptable for one of the candidates to change the rules of the game at the last minute in order to assist his candidature at the expense of other competitors," spokesman Mr Learnmore Jonge said.
"We would want the court to arbitrate as a matter of urgency," he said, adding that his party would bring the legal challenge tomorrow.
Mr Jongwe said President Mugabe had abused his powers in passing the regulations.
President Mugabe, up against his first real challenge after 22 years in power when he faces MDC leader Mr Morgan Tsvangirai at the weekend, made the regulations retrospective to last Friday.
Under his decree, potential voters have to prove they are residents of a constituency in which they will be casting their ballots, a measure more likely to affect urban dwellers, who tend to support the MDC.
Many urban dwellers are not homeowners and will be unable to prove their residency, according to Zimbabwe Election Support Network (ZESN) spokesman Mr Tawanda Hondora.
In rural areas, voters can get traditional leaders to vouch for them. The government recently awarded huge perks to village elders.
"He (Mugabe) is amending the electoral law himself, notwithstanding that he is a candidate himself," Mr Hondoro said.
The laws also mean only 22,000 government-appointed election monitors -including soldiers - will be authorised to take action on irregularities that occur during the polling.
Foreign and local observers cannot intervene, but they can ask official monitors to correct irregularities, according to Mr Douglas Nyikayaramba, the chief election officer of the government-appointed Electoral Supervisory Commission (ESC).
Mr Nyikayaramba claimed that all election monitors were impartial, despite being civil servants and military officers.
Mr Reginald Matchaba-Hove, head of ZESN - a coalition of 38 civic organisations - criticised the way in which the new rules were introduced.
"This has only served to create confusion in the whole electoral process," he said.
Mr Matchaba-Hove said the use of soldiers as monitors was a "stark contradiction" of Southern African Development Community (SADC) electoral norms and standards.
President Mugabe's order restored amendments the Supreme Court had declared invalid and added an unknown number of ruling party supporters to the voters' roll, according to Mr Welshman Ncube, MDC secretary general.
The order also left the door open to more unannounced changes in the electoral system, according to Mr Ncube. "Anything done in the past and anything done in the future" will be valid under the law, he said.
"It simply allows them to act in terms of a non-existent law," he said.
The MDC's Mr Paul Temba Nyathi claimed the new laws are "all carefully designed to cheat the MDC of its victory."
The government, meanwhile, has designated 4,548 polling stations across the country for the 5.6 million registered voters, but it was not clear today where they would be located.
State television announced that the list of polling stations would be published from Thursday through to Sunday.
The authorities have accredited fewer than 1,000 independent poll watchers - 300 local and 560 foreign observers.
And with just three days to go to until the voting starts, the electoral roll is still at the printers, according to the government's chief poll organiser, registrar-general Mr Tobaiwa Mudede.
However, there are no laws governing when the electoral roll should be published, only that it should be ready on voting day, according to specialist lawyer, Mr Lovemore Madhuku.
AFP