The UP Express train service between Union Station in downtown Toronto and Pearson International Airport near the city resumed Sunday morning after cancelling all trains on Saturday due to “service issues.”

In a statement issued Saturday evening said the UP Express, which connects the airport with the major downtown rail hub, will resume 30-minute service between the two sites while making all stops beginning Sunday at 6 a.m.

Authorities with Pearson said earlier in the day that the link connecting the site with Union was “experiencing service issues” and not operating, announcing the temporary suspension of the UP Express in a tweet around midday.

UP Express operator Metrolinx said in a statement that none of its trains along that line would run Saturday, though it did not provide a reason for the shutdown and said shuttle buses were available at Terminal 1 of the airport.

The UP Express says it has now “made some necessary repairs” to its trains.

The TTC says it has increased service on its 900 Airport Express route for the remainder of this weekend for travel to and from Pearson International Airport.

It said that beginning early Saturday evening, buses will be operating between Kipling Station and Pearson International Airport every eight minutes or less.

In a statement issued Friday, Metrolinx said its workers “discovered hairline cracks in the brake discs” on some of its UP Express trains during regular inspections last weekend.

It said it immediately removed the affected trains from service and began inspecting the rest of its fleet.