If found guilty, the two could be sentenced to five years in jail and fined.

According to NBR sources, Tarique and Koko paid Tk 44 lakh in taxes and fines to legalise undeclared income on July 28.

Their family lawyer paid the money to Bangladesh Bank through a money order. Tarique, who is in jail now, paid Tk 5 lakh to legalise Tk 18 lakh undeclared income and Koko paid Tk 39 lakh to legalise over Tk 1.5 crore undeclared income.

A certified copy of the pay order was sent to Circle 18 tax office under Tax Area-6 as receipts for the payment.

But, the tax office refused to accept it since the two had not followed proper rules and were listed as corruption suspects by the Anti-Corruption Commission.

Later, another application was rejected on the grounds that income tax details were not provided in accordance with approved procedures and for failure to submit a tax return form, sources added.

NBR sources said the application of Tarique and Koko to legalise undeclared incomes was rejected because several extortion cases against Tarique are currently under trial and similar accusations are also there against Koko. The central bank has also requested details of the two brothers' bank transaction.

Khaleda Zia's lawyer Shimul Biswas yesterday said, "Tarique Rahman and Arafat Rahman have applied to legalise their undeclared income by following the correct legal avenues."

On July 31, Khaleda also paid Tk 34 lakh to legalise around Tk 1.33 crore undeclared income, but the NBR did not immediately accept the application on the grounds that due process was not followed. Khaleda again submitted her income tax details on Monday to legalise undeclared income.