Federal Opposition Leader Tony Abbott has revealed the Coalition will not fund Brisbane's Cross River Rail project if it wins government, prompting an early election issue for the people of south east Queensland and sharp criticism from state Labor.

The project, in planning for five years, would provide a second rail crossing from Brisbane's southside to its northside.

The city's only rail crossing will become choked in 2016, both political parties have agreed.

In Tuesday's budget federal Labor agreed to a written request from the Queensland Government to provide $715 million over the next six years, plus a concession on GST payments in order to start the project.