(CNN) -- A Swiss court Friday blocked Switzerland's largest bank from turning over account information to the U.S. government under an agreement reached earlier this week in which the bank, UBS, admitted it had helped U.S. taxpayers hide money from U.S. tax authorities.

Attorney Andreas Rued filed suit earlier Friday seeking an injunction to prevent the data transfer, he told CNN, and received the Swiss Federal Administration Court's decision within hours.

"The customer data may not be given out," he said, "to protect the interests of the customers."

The Swiss financial oversight authority, Finma, had asked UBS to transfer the data, according to Rued, and now Finma has until Tuesday to submit a written opinion challenging the court's decision. The court will read the opinion and then decide on whether to leave the restraining order intact, he said.

The U.S. Justice Department announced Wednesday that UBS had agreed to pay $780 million in fines and restitution and to turn over the account information. The agreement was approved by a federal court in Fort Lauderdale, Fla.

The department cited a ruling by Swiss authorities that forced the bank to make the "unprecedented" disclosure of names of account holders, and it promised to drop a criminal charge against the bank if it complied with all terms of the agreement.

UBS Wednesday issued a statement in which Chairman Peter Kurer said, "We are firmly committed to the terms of the settlement agreements we have reached" with both the Justice Department and the U.S. Securities and Exchange Commission.

However, it appears only a small number of accounts may have been included in that agreement.

On Thursday, the government filed suit against the bank to force it to give the Internal Revenue Service secret account information on thousands of accounts believed to be worth nearly $15 billion.

The lawsuit filed Thursday in Miami says that as many as 52,000 U.S. customers had secret UBS accounts to allegedly hide holdings from the IRS. About 32,000 of the accounts contained cash and 20,000 contained securities, it said.

After the lawsuit seeking additional names was filed Thursday, UBS (UBS) issued a statement saying that it will "vigorously contest" enforcement of the IRS summons in the suit, and that contesting the summons is permitted under the agreement announced Wednesday.

"The IRS's 'John Doe' summons seeks information regarding a substantial number of undisclosed accounts maintained by U.S. persons at UBS in Switzerland, whose information is protected from disclosure by Swiss financial privacy laws," said the new UBS statement.

The IRS on Wednesday issued a statement warning the U.S. customers of the bank that they would be pursued if they did not step forward and pay what they owed.