Nigeria's President Bola Tinubu has asked the Senate to approve an additional spending of 6.2 trillion naira ($4 billion) to plug shortfalls in this year's national budget, according to a letter read to lawmakers on Wednesday.

Tinubu also sought to impose a one-off windfall tax on banks' foreign exchange gains, as his government aims to raise revenues to fund "capital infrastructure development, education, and healthcare as well as welfare initiatives."

Senators immediately started debating a bill to approve the extra spending request, which comes at a time when the government is under pressure from unions to agree on a new minimum wage amid the country's worst cost of living crisis in a generation.

Lawmakers had passed a 28.77 trillion naira budget for 2024 in December, the first full-year spending plan under Tinubu.

Tinubu's request is in line with provisions in an "Accelerated Stabilisation and Advancement Plan" (ASAP), drafted by the finance ministry with private sector executives and some economists, that aims to address challenges related to reforms aimed at boosting growth.

Last May, Tinubu axed a popular but costly subsidy on petrol and twice devalued the naira in landmark reforms cheered by investors to try to kick-start growth. But the move caused petrol prices to triple, increased transport costs and pushed inflation to a 28-year high, angering citizens.

Tinubu has faced pressure from labour unions over the rising cost of living due to his reforms, but he has vowed not to roll them back.

The president told lawmakers that 3.2 trillion naira from the extra spending will go to build "critical infrastructure projects" across the country and 3 trillion naira will fund "further recurrent expenditure requirements".

Nigeria's economy has been stuck in low gear with growth of around 3%, far short of the 6% annual expansion Tinubu targeted when he came to power last year.

Tinubu has asked his economic management team to prepare a 2 trillion naira stimulus plan to address concerns about food supplies, and bolster key sectors such as energy, health and social welfare.