Mr Ban said migrant labour was good for economies
The threat posed by the global economic crisis to the world's estimated 200 million migrants should not be forgotten, the UN chief has warned.
Ban Ki-moon warned that migrant workers in construction and tourism industries were already being badly hit, with a knock-on effect on global remittances.
He highlighted growing public hostility to migrants in industrialised countries as the crisis develops.
Mr Ban was speaking to a conference on migration in the Philippines.
"Today, we face a cascade of national financial crises throughout the world. None of our economies are insulated," Mr Ban told the Global Forum on Migration and Development in Manila.
Mr Ban highlighted growing personal hardship and anxiety in many countries, as a result of slowing growth or recession.
"Given these developments, it would be naive to think the current crisis will have no effect on the movement of people across borders, and on how publics perceive migration and the migrants in their midst," he said.
Mr Ban said there were already signs that flows of remittances - an important source of revenue for poor countries as diverse as the Philippines, Mexico, Bangladesh, Tonga and Moldova - were slowing.
Governments in industrialised nations were under pressure to curtail immigration amid rising unemployment, he said, but such measures would be short-sighted.
Mr Ban argued that mobile labour markets were beneficial to economies and clamping down on immigration would only spur increased illegal immigration.
"Migration will flow through unsafe and irregular channels. This will undermine confidence in our ability to govern - confidence that has already been damaged by the financial crisis," Mr Ban added.
Philippine President Gloria Arroyo echoed his words, urging delegates not to "lose sight of the poor" in the focus on tumbling global stock markets.
According to a study published last year, migrants sent home $301bn (£187bn) in remittances in 2006 - a huge sum of money that exceeds aid and foreign direct investment put together.
Such revenues are of greatest importance to Asia and Latin America and the Caribbean, the study suggested.