Rail links from Inverness, Aberdeen, Dundee and Perth are lagging far behind those between their central counterparts, warned the Scottish Association for Public Transport (SAPT)
Glasgow and Edinburgh are already set for an upgrade by 2018, when eight minutes are due to be cut from 50-minute journey times by a new electric train fleet.
Stirling, Dunblane and Alloa will also benefit from upgrades to the electrification of lines which is due to be included in the next ScotRail franchise in 2015.
However, SAPT says Transport Scotland should also include specifications in next year's invitation to tender for an upgrade of services linking northern cities and the central belt.
Chairman Dr John McCormick said: "The new ScotRail franchise to start in 2015 is expected to last for up to 10 years.
"This is a once-in-a-decade opportunity for a step-change in train travel in the Highlands, the north-east, and Tayside.
"We urge Transport Minister Keith Brown to ensure the whole of Scotland benefits from much better rail services from 2015, not just the central belt."
Rail travel north of the central belt also has more to compete with in terms of road travel, with large investment in many routes, including the £3 billion upgrade of the A9. SAPT say that with high performance trains and infrastructure upgrades, transport chiefs should aim to cut journey times by 20%.
Liz Cameron, chief executive of the Scottish Chambers of Commerce said that rail links north of the central belt did not adequately serve the needs of the Scottish economy.
She said: "The lines connecting Inverness and Aberdeen with the central belt and with each other suffer from single-track sections which compromise the ability of rail operators to deliver the kind of services businesses need.
"More and more people are using rail services in Scotland and investment to enhance capacity is required if Scotland's cities and regions are to be adequately connected."
A spokesman for the Government transport agency said the invitation to tender, setting out the specification for the franchise, would "reflect the Scottish Government's commitment to providing enhanced rail services across the whole of Scotland".
He added: "Bidders for the next ScotRail franchise will be required to demonstrate how they will improve the comfort and suitability of trains operating on longer distance routes, including services from the central belt to Inverness and Aberdeen."
Derick Murray, director of Nestrans, the transport partnership for Aberdeen city and shire, said it had met bidders for the tender and had "highlighted the principle of reducing journey times between Aberdeen and the central belt as a key objective".
Eric Guthrie, director for the Tayside and Central Scotland Transport Partnership (Tactran) said progress on improvements was something the organisation was continuing to press for, while Frank Roach, manager for the Highlands and Islands Transport Partner ship (Hitrans), said it was engaging with bidders to discuss their priorities including rolling stock and faster journeys.