Train services in Wigan and the north west are making passengers ill, according to Mayor Andy Burnham.
The former Leigh MP has now written to Transport for the North (TfN) to highlight a series of missed pledges and examples of poor performance, said to have occurred on operator Northern's watch.
Commuters have "bombarded" the Mayor with complaints during the early months of 2018 and he now says "enough is enough" and wants the transport body to step in.
His intervention comes just days after Wigan MP Lisa Nandy called for the route to be renationalised, amid growing disquiet over problems with the Northern franchise.
Mr Burnham said: "Enough is enough. Northern passengers, the people of Greater Manchester, deserve so much better than the dire service they have been forced to endure in recent months.
“I am calling for TfN formally to assess whether Northern is in breach of its franchise agreement.”
In his letter to John Cridland, the TfN chairman, he has cited the operator on a number of grounds, including their alleged failure to increase the number of trains per hour on some routes and launch refurbished bi-mode trains between Wigan North Western station and Manchester Airport.
Mr Burnham added: "I believe Transport for the North should now consider escalating its response and assess whether Northern are in breach of the performance targets as set out in its franchise agreement."
Passengers have complained to the Mayor that overcrowding on trains in the region has caused illness and discomfort
The Mayor added: "How can it be right that Northern presides over a service on which dangerous overcrowding in rush-hour is the norm, to such an extent that we know passengers have been taken ill? What accountability exists for an operator so persistently failing in its duty to deliver a reliable, safe service?
"The time has come to increase pressure on Northern to start delivering for its customers."
A spokesman for the Rail Delivery Group, which incorporates Northern, said:"Everyone wants a great railway for the north of England. That’s why Northern is in the early stages of an ambitious transformation programme to modernise services across the region, improving journeys, better connecting communities and boosting local economies.
"As with all major transformation projects there have been challenges and there may be more to come but teams are working together tirelessly day-in-day out to minimise any disruption to passengers.”
Responding to criticisms by Ms Nandy and fellow MPs previously, a Northern spokesman said the current delays had been caused by driver shortages as a result of issues with the electrification of the Blackpool line.
He added: "We appreciate this is a far from ideal situation which is causing some customers frustration and disruption, which we’re sorry for
"We can assure you that we’re doing everything possible to get back to the good level of service you expect and deserve."