The 'Operation Magnify' campaign was launched by Immigration Enforcement in October to stamp out illegal working in 'risk' industries.
The drive was carried out in partnership with other government agencies including HMRC, the Health and Safety Executive and the Gangmasters Licensing Authority.
The first phase targeted the construction industry between 11 – 18 October.
Officers conducted 69 enforcement visits, resulting in 257 people being arrested at building sites and residential addresses.
It is understood around two thirds of suspects were Indian nationals, however other nationalities included Albanians, Pakistanis and Nigerians.
Referral notices were issued to nine businesses warning they may be liable for financial penalties of up to £20,000 per illegal worker.
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One visit to a Chester building site, operated by Sword Construction, resulted in 20 illegal workers being arrested.
The potential penalty currently under consideration is £400,000, the largest of the campaign.
Steps are now being taken to remove those arrested from the UK.
Immigration Minister James Brokenshire said: "Illegal working undermines legitimate employers, drives down wages and denies employment to hard-working UK citizens and legal migrants.
"Operation Magnify is all about disrupting illegal working and making life impossible for employers who do not play by the rules. The results show that the cross government approach is working.
"We are sending out a strong message by extending this initiative to other employment sectors. While we are happy to work with those businesses to help them carry out the right checks on their staff those who do not play by the rules could face severe financial consequences."
Mr Brokenshire added the current Immigration Bill going through Parliament will lower the existing evidence requirement for cases, making it easier to prosecute employers who are aware an employee cannot work in the UK.
"We are also increasing the current maximum sentence from two to five years and introducing new powers to close businesses or have their licences removed," he added.
It is understood 'Operation Magnify will continue throughout 2016 and be extended to other illegal working sectors, such as taxi and private hire drivers, street markets, catering and agriculture.
(LM)
