Mick Cash, seen by many as the front runner to succeed the late Bob Crow as head of the 80,000-member union, said he would lodge claims with rail chiefs for a basic 32-hour week.
It could lead to strikes and disruption to help win a better work-life balance for workers in the coming months, Mr Cash warned, as ballot papers for a vote on the general secretary role were dispatched to RMT members.
However a Scotrail insider said immediate disruption was unlikely as pay deals were already in place.
Mr Cash is currently acting general secretary of the RMT, after serving for 12 years as Mr Crow's deputy. He said a shorter working week would give thousands of transport workers more time off, increase hourly pay rates and create thousands of jobs.
He said it offered an alternative to plans by some employers to cut staff - plans he said were being encouraged by the Government.
Mr Cash claims to have secured the biggest number of nominations for the top job among the union's Scottish branches
He said: "Transport bosses are raking in massive profits and bonuses while rail and bus workers work long, unsocial hours keeping our transport network moving all year round.
"My aim is to negotiate a basic 32-hour week for all our members so that they can spend more time relaxing and with their loved ones, and the truth is that the employers can easily afford it, because they are awash with cash and will become even more so as the economy grows."
He said it would be up to transport bosses whether his proposals resulted in disruption. "I hope that employers will embrace our claim, but if they refuse to address it there could well be widespread industrial action and that will inevitably mean disruption for passengers.
"But shorter hours means more jobs and a safer and more productive workforce, and that will benefit transport users and the wider economy as well as loyal transport workers."
The RMT also represents thousands of workers in offshore energy and shipping, and Mr Cash also called for better leave and improvements in safety for offshore workers and seafarers.
"Instead of squeezing workers to maximise profits for the few, our multibillion offshore and shipping industry should make a massive new investment to improve safety and give more time off for its workforce," Mr Cash said.