The prohibition could become permanent unless the party's leadership supplies more information about its activities.
Social Democrats are accusing officials of the kind of authoritarianism that has long dominated politics in neighboring Uzbekistan -- where opposition groups are harassed and pro-government parties fill the landscape.
Social Democrats have long been critical of President Emomali Rahmon's administration. Most recently, the Social Democrats were among several parties that dismissed as illegitimate the presidential election in November that handed Rahmon a new seven-year term.
Now the Justice Ministry accuses the party of failing to provide an obligatory annual report and has asked the Supreme Court to ban its activities for half a year.
Pulling Together
Social Democrats have been joined by other opposition politicians in describing the ministry's accusation as the latest effort to pressure government critics and independent groups.
Opposition politician Rahmatulloh Valiev, whose own Democratic Party was torn apart by a rift over support for the administration, tells RFE/RL that he thinks it is the Social Democratic leaders' criticism of the government that most concerns the authorities.
"[The Social Democratic Party] had dubbed the last presidential election unlawful," Valiev said. "In the past, the party's leader, [Rahmatulloh] Zoirov, had written to the Supreme Court that President Emomali Rahmonov (Rahmon) has been holding the post of president unlawfully."
The party argues that a referendum that extended presidential terms to seven years was invalid, and that Rahmon should therefore have left office in 2004.
Justice For All?
The Justice Ministry stresses that Tajik law requires all political parties and groups to file a report with the ministry, providing a full account of their activities.
Davlat Sulaimonov, the ministry official responsible for party registration, said the ministry has repeatedly asked the leader of the Social Democrats to supply the required report.
"Rahmatullo Zoirov had personally signed that he received our written warning," Sulaimonov said. "We asked him several times to provide the report to the ministry. But the party did nothing to solve existing problems. So we sent a letter to the court."
But Social Democratic Deputy Chairman Shokirjon Hakimov dismissed that account.
"We have submitted the written report," Hakimov said. "But as far as I know, the authorities asked for more documents which are not required by law -- such as the number of party members, the number of party members in each district, and so on."
Familiar Refrain
Valiev said it is not the first time that Tajik authorities have tried to weaken or eliminate opposition groups. He claims officials use legal avenues or meddle in parties' internal affairs.
Tajikistan's Development Party has sought unsuccessfully to register with the Justice Ministry since 2002.
One major opposition party, the Socialists, split into rival wings in 2005 in a move initiated by members who backed the government. The pro-government wing was then granted registration by the Justice Ministry, inheriting the party name as well.
A split of the Democratic Party ahead of Rahmon's reelection in 2006 followed the same script.
Opposition politician Valiev accused the government of trying to create an opposition-free political environment -- like in neighboring Uzbekistan or Turkmenistan. He says Rahmon's administration works to weaken rivals and replace them with pro-government parties.
"If these pressures continue, and if the government does not change its position regarding political parties, it is possible that Tajikistan will be turned into a country like neighboring Uzbekistan or Turkmenistan," Valiev said.
But Valiev also noted that it would be difficult for the government to exclude all true opposition parties from the country's political life. He said that after more than 15 years of activity in post-Soviet Tajikistan, independent-minded politicians will not give up easily.
(RFE/RL Tajik Service broadcaster Mirzo Salimov contributed to this report.)