Argentina anti-austerity strike brings country to standstill
The General Confederation of Workers is also demanding salary hikes in line with inflation of nearly 30% a year.
Trains, buses and the underground system stopped in Buenos Aires. Access roads to the capital were blocked by activists.
Some 15 million people were affected in the capital, officials said.
Flights were suspended across the country. Mr Macri said he took the decision to avoid an economic crisis.
"The strike does not contribute to anything," said Mr Macri.
"Our economy will start growing again, but for that we need to sit round the table and decide what each one of us has to do," he added.
The unions say they are willing to negotiate.
"There is a new opportunity and I hope the government has understood what today's strike means," said Carlos Acuña, one of the leaders of the General Confederation of Workers.
Argentina's relationship with the IMF is rocky.
Many blame the international lender for causing tough economic conditions in the country when Argentina defaulted on its debt 17 years ago, says the BBC's Katy Watson.
The unions say the austerity measures demanded by the IMF to agree the loan will bring hardship to the poorest in the country.