Tax revenues in January fell 13 percent from the previous year to 3.44 trillion yen, the largest monthly decline since the start of fiscal 2001, the Finance Ministry said Friday.
It was the fifth-straight month in which tax revenues fell.
Cumulative tax revenues for the fiscal year through January came to 31.52 trillion yen, down 1.2 percent from the same period the year before.
January was the first month in fiscal 2001 for combined tax revenues to fall below the level from the year before.
In the month, corporate tax revenues fell 6.7 percent to 240.69 billion yen.
Income tax revenues fell 19.6 percent to 1.93 trillion yen, with revenues from tax withheld from wages down 19.8 percent to 1.91 trillion yen and those from tax on declared income down 4.5 percent to 19.39 billion yen.
A ministry official attributed the decrease in overall tax revenues to falls in tax levied on maturing long-term postal savings, while others blame the nation's wilting economy.
"Overall," the official said, "we are on a path to achieve the revised tax revenue projection."
The ministry has downwardly revised its tax revenue projection for the current fiscal year by 1.1 trillion yen to 49.63 trillion yen, largely because of falling corporate tax receipts.
Many companies are expected to report further deterioration of business performance because of the economic slump, and tax revenues will likely suffer accordingly, economists say.
A large number of companies pay corporate taxes after they close their books at the end of the month.