A glass-covered, underground path opens Sunday for TTC commuters at Union Station, after the lower level closes for construction.

In a news release, Metrolinx said passengers will be rerouted to the north exit of the York Concourse so the city to can continue its revitalization project, which will last until December 2019.

Bruce Hawkins, a senior spokesperson for the City of Toronto, said more than 300,000 commuters pass through the station every day and the city knows even more are coming.

"It needs to accommodate the commuting traffic of today but also the future commuting traffic, which we know is going to increase in the future," Hawkins told CBC on Friday.

Some of the work to be completed over the next six months includes:

The glass roof in the east Front Street moat.

The new stairs to the Bay retail level (below the future Bay Concourse).

Improved access to the TTC subway station.

Twelve additional retail spaces in the station.

"The city's work will improve the transfer for GO and TTC customers at Union Station," Anne Marie Aikins, the senior manager of media at Metrolinx, told CBC Toronto Thursday.

"But any change for commuters can mean an adjustment period so we, the city and Metrolinx, prepare well in advance with communications and signage. We will also have additional staff next week at the station to help guide people."