PRAGUE, Jan 5 (Reuters) - Czech natural gas transmission system operator Net4Gas (N4G) has not received the latest monthly contracted payments from a major Russian shipper, it said.

Net4Gas's revenues from the contracts accounted for three quarters of total 2021 revenue, the company said in a filing late on Wednesday.

"N4G is currently investigating the reasons for this non-payment, which in N4G’s view represents a contractual breach on the part of the major shipper," it said.

"N4G further notes that it is currently able to cover its ongoing operating and financing costs."

The company did not name the shipper and could not be immediately reached for further comment. (Reporting by Jason Hovet Editing by Mark Potter)