BUENOS AIRES (Dow Jones)--A local judge's demand that an Argentine opposition leader testify in a drug-trafficking case is fueling accusations of dirty politics in an increasingly acrimonious electoral campaign.

On Monday, Federal Judge Federico Faggionato Marquez cited Francisco de Narvaez, who heads a list of candidates up against one headed by former President Nestor Kirchner in a battle for 35 lower house Buenos Aires province seats, to testify in a case concerning ephedrine trafficking. It concerns claims that a cellphone listed in de Narvaez's name was recorded making calls in 2006 to the so-called "King of Ephedrine," Mario Segovia, who is currently behind bars.

De Narvaez, whose campaign says the phone in question was not under his control, is refusing to abide by the judge's demand, calling it a "political operation" instituted by the government of President Cristina Fernandez, Kirchner's wife.

De Narvaez's Union Pro party was supported in this response by leaders of the Acuerdo Civico y Social alliance. In comments to La Nacion newspaper, Gerardo Morales, the leader of the Union Civica Radical, noted that Faggionato Marquez has 36 outstanding malpractice denunciations against him. He called it "suspicious that he would come out now with this citation" just before the June 28 mid-term elections.

But in televised comments Tuesday, Kirchner was unrepentant.

"To say that the justice system is not independent is a simplistic political act that is truly dangerous and unacceptable," said Kirchner, who called on de Narvaez to face the judge, "like any other citizen."

Shortly afterward, de Narvaez was back on the airwaves, saying that he "is prepared to front any judge that we consider independent" but not Faggionato Marquez.

He accused Kirchner and the government of hypocrisy, citing a host of corruption cases in which government ministers have not been forced to testify. In particular, he noted the case of Venezuelan-American Antonini Wilson, who was caught trying to smuggle $800,000 and who later declared in the U.S. that he did so at the behest of Argentine and Venezuelan officials.

The case is adding to other claims of dirty tactics against the Kirchner-Fernandez campaign as it tries to protect the government's majority in the Congress.

It started with the expediting the election by moving it up four months to June 28, a shift that will extend the lame-duck Congress period from two months to six. President Fernandez said she did so to avoid having politics distract the government from the task of confronting an economic crisis. But the opposition - which unsuccessfully tried to rally Congress to disapprove the change - claimed she was seeking only to minimize fallout from a deteriorating economic situation.

Then there were claims that Kirchner was ineligible to run because he changed his residential address from the province of Santa Cruz to Buenos Aires too recently. Despite challenges, his candidacy was accepted on the grounds that he will have been registered as a Buenos Aires resident for the required two years when he takes office in December.

The campaign has also seen the phenomenon of "testimonial candidates:" star names like Buenos Aires Governor Daniel Scioli and actor Nacha Guevara added to Kirchner's list of fellow candidates even though they are widely expected to never take office. Two judges have already turned down opposition efforts to ban those candidacies, arguing that there is no way to determine ahead of time whether they truly intend to take office or not.

Then there's the case of Fernando Jesus Narvaez, whose name appeared at the top of a separate opposition list. The de Narvaez campaign says this man's name was deliberately included to confuse people and draw votes away from the Union Pro leader. Fernando Narvaez avoided press contact for days but was eventually tracked down late last week. He was quoted in one interview saying he had "no interest in politics."

Meanwhile, there have been various accounts of dubious national documents known as DNIs, the presentation of which is needed for a person to cast a vote. Expressing concerns over the risk of double-voting and miscounting, de Narvaez's campaign has been running TV ads calling on people to stand up for their right to vote.

The tension over these issues comes as a variety of polls suggest a close race.

In a poll from the closely followed Poliarquia group published Sunday, de Narvaez had a three-point lead over Kirchner in the province. Other pollsters have had the ex-president in the lead by a similar margin.

Whether or not Kirchner leads the final vote tally in the province, it seems likely that the majority of the votes will more or less be shared by de Narvaez and another list led by Acuerdo Civico y Social candidate Margarita Stolbizer. Under Argentina's proportional representation system, it means the government will get a minority of the 35 Buenos Aires seats up for grabs in the lower house.

With official candidates expected to lose votes in other parts of the country, many analysts are predicting that the government will lose the congressional majority it has enjoyed for the past four years, a change that is expected to make it much harder for Fernandez to govern.

-By Michael Casey, Dow Jones Newswires; michael.j.casey@dowjones.com; 54-11-4103 6740