Sadiq Khan has slammed the Government's new visa rules for foreign workers as an "economic own goal" and detrimental for London.
The Mayor on Wednesday said migrants were "critical" to the capital's public services and Britain's economy.
Earlier this week the Home Office announced that new minimum wage thresholds for foreign worker visas will come into force "within weeks".
Mr Khan said: "Pulling up the drawbridge on thousands of foreign workers and their families is the latest example of the Government pursuing damaging economic policies in order to look tough on immigration.
"Migrants are critical to London and the nation’s economy and public services.
"We should be supporting foreign skilled workers who want to come here and fill roles vital to our economy – not making it tougher for them. I am worried this will have a really detrimental impact on sectors such as hospitality and social care.
"These further restrictions represent another economic own goal from the Government."
Reforms to restrict care workers from bringing family members to the UK will come into force on March 11.
Measures requiring care providers to register with the Care Quality Commission if they are sponsoring migrants will start on the same date.
An increase in the minimum salary required for those arriving on a Skilled Worker Visa, from £26,200 to £38,700, will start from April 4.
The minimum income threshold for those bringing dependents to the UK on family visas will increase in stages starting on April 11. From this date workers will need to be earning at least £29,000-a-year to bring a family member from abroad - up from £18,600.
Some 6.2 million foreign-born people were employed in the UK at the end of 2022, making up nearly a fifth of the working population.
Migrants are overrepresented in the hospitality, transport and IT sectors and are more likely to work during night shifts and in non-permanent jobs than the UK born residents, data from the Migration Observatory and the Trust for London shows.
A source close to Conservative Mayoral candidate Susan Hall said: "Once again Sadiq is carping on about things outside his brief.
"With crime running rampant, the Ulez slamming Londoners to the tune of thousands, and his share of taxes on the rise - the Mayor should focus on the day job."