Sinn Fein is pressing for Belfast City Council to ask Europe for up to £3bn - before the UK leaves the EU.
Councillor Jim McVeigh proposed the council works alongside Dublin City Council and the Department for Infrastructure to ask for the huge sum to upgrade the rail link between the two cities.
Travelling the 100-mile distance between Belfast and Dublin by train currently takes around two-and-a-half hours due to lower speed limits in sections of the track.
Mr McVeigh - who travels between the two cities regularly through his trade union work - said a quicker rail connection could "transform the island economy".
His motion was seconded by Alliance councillor Michael Long.
"The council believes that a high-speed rail connection between Belfast and Dublin, reducing travel time to just one hour each way, would help transform the island economy to the specific benefit of both Belfast and Dublin," Mr McVeigh told the council.
He estimated that the upgrade could cost up to £3bn. "One of the most important reasons why we want to suggest this, is because this is one of those occasions when we might be able to get someone else to pay for it," he said.
"In bringing this motion forward we did go and talk to our MEPs, we sought advice from those who know the European Institutions and the Juncker Fund in particular, and they have assured us that this proposal is a very credible proposal, and that this proposal is exactly the sort of proposal that the fund was set up to accommodate.
"Even if you take Brexit into account, we are talking about 2019 before the London Government would take us - this part of the island - out of the EU.
"Two thirds of that route would remain in the EU, so we think there is a valid case for both states on this island to apply for this funding.
"We all make proposals on this council which are a little bit of grandstanding, but on this occasion we want to make it clear that this is a very real proposition.
"We are not doing it for the optics, we are doing it for the economic benefits and primarily to draw down perhaps £2-3bn for a project like this across this island."
Mr Long said he was happy to second the motion, adding that due to the "financial and economic instability likely to come about" after Brexit, it is important that Belfast does "whatever we can to mitigate that issue" and "build a stronger economy".
He noted the 200mph speeds that trains in Japan travel at, adding that Northern Ireland is "very far behind".
The motion was referred to the council's City Growth and Regeneration Committee, which will meet next Wednesday, October 12.