Jeremy Corbyn says plans to manufacture parts for a £2bn wind farm off the Fife coast at a site thousands of miles away are not credible.
It comes after energy giant EDF said no Scottish company had the capability to manufacture and supply the steel required for the Neart na Gaoithe site.
Mothballed manufacturer BiFab had hoped to secure the work to build wind turbine jackets for the project.
There is growing speculation the work will be done in Indonesia.
The GMB and Unite unions have been campaigning for the work to come to the Bifab yards in Methil and Burntisland, a few miles from where the new wind farm will be created.
EDF said it was currently in a structured procurement process, which started with tier one contractors who would deliver large sub packages of the NnG project.
The French-owned energy giant said it was working closely with its tier one preferred suppliers to encourage them to use Scottish suppliers for tier two work packages, such as the manufacturing of some of the jackets for the turbine foundations and the manufacturing of towers.
A spokesman for EDF said: "It is essential whichever supplier is chosen that they are competitive so UK energy consumers are not overpaying for their energy."
The issue was raised at an event in Kirkcaldy on Saturday, where the UK Labour leader addressed workers and trade unionists at a rally following the Fighting For Our Future march.
Mr Corbyn, who called for a "Green industrial revolution", said it was not credible to "drag" manufactured parts 8,000 miles to the wind farm site.
He said: "Allocation of work is a very important issue indeed.
"It really is not credible to say that it's the right thing to do to build facilities that will be used for the generation of electricity on wind farms in the vicinity, almost in sight of the coast, and you're dragging the manufactured parts to make those wind turbines 8,000 miles by sea with steel that's probably come from 10,000 miles away.
"Where is the sustainability in that? The sustainability is in using the local skills, using the local knowledge, using your own manufacturing capability and developing the infrastructure that goes with it, and so we as a party are working very hard on the principles of what I call a green industrial revolution."
Scottish Greens Fife MSP Mark Ruskell also addressed the STUC rally.
He said there should be no offshore wind farm leases issued from the Crown Estate without the guarantee of local jobs, and that government subsidies should be conditional on local input.
He added: "We can't rely on the dead hand of the free market to grow jobs. Oil and gas companies will extract every last drop until production goes over the cliff and takes communities dependent on the jobs with it."