The City has fired off an email to businesses that are required to offer commuter benefits to their employees under a new city law that went into effect in January.

That says: “Over the next couple of months two large Muni changes will occur that may impact your business and employees.”

Since Muni will increase the cost of Fast Passes, employers covered by the commuter benefit law “will be required to begin offering a subsidy of $70 or more per month starting in January 2010.”

In January, Muni will offer two Fast Pass options:

*A $70 option to ride Muni and BART (within San Francisco)

*A $60 option to ride Muni only

The email, sent by the Department of Environment’s Clean Air and Transportation Program, also warns: “Starting December 5th, there will be major Muni Service changes, which may impact your employees. Please share the following SFMTA announcement with all Muni riders at your company.”

That announcement says that Muni must make service changes to help close a $129 million deficit.