The Justice Department has opened a criminal investigation into small Swiss regional banks which may have helped Americans evade taxes, the New York Times reported, citing two people briefed on the matter.

The investigation will also look at Wall Street banks that provide banking services to these regional banks, known as cantonal banks, the paper said in an article published on Thursday.

The Wall Street banks might have been used by the regional banks to pool client money so individual clients could not be identified by U.S. authorities, the paper said.

A spokesperson for the Justice Department was not immediately available. The department was closed on Friday for the Christmas holiday.

The new investigation will focus on Basel-based Basler Kantonalbank, the paper said.

Earlier this month a former UBS banker pleaded guilty to charges he helped wealthy American clients hide their money from U.S. authorities. Renzo Gadola, a Swiss citizen, was charged with helping clients shift their undeclared money from UBS accounts to Basler Kantonalbank.

(Reporting by Yinka Adegoke and Jeremy Pelofsky; Editing by Andrea Ricci)