At least 304 coronavirus cases have been linked with people working at food processing sites in Wales.
Health minister Vaughan Gething said that many staff were working on low wages, which meant they could be reluctant to take sick leave if they became ill.
There are now 200 cases of Covid-19 associated with the 2 Sisters chicken processing plant in Llangefni, Anglesey, including household contacts of staff, and 70 confirmed cases with the Rowan Foods factory in Wrexham.
On Tuesday, Mr Gething revealed an investigation was also underway at the Kepak meat processing plant in Merthyr Tydfil, which is not classed as an outbreak, where there had been 34 confirmed cases since April 25 including eight since June.
He told the Welsh Government's daily press briefing: "In the meat processing sector, margins can be tight.
"Many people are employed on fairly low pay, and levels of statutory sick pay mean that many people feel as though they have no choice but to carry on working even when they're ill."
Mr Gething said a meeting with unions would take place later this week to seek information on "appropriate communication methods" to help meet the health and safety needs of workers at each of the sites, while he planned to publish safety planning guidance for the sector later this week.
He said said outbreaks in food processing plants were a feature of the pandemic "around the world", including the USA and Canada, with an outbreak in Germany affecting more than 1,300 employees.
But Mr Gething said there were no signs the outbreaks at the two sites in North Wales had spread into the surrounding communities.
"I want to repeat these are outbreaks centred on the plants themselves, and at present there is no wider community transmission," he said.
"But we are, as you would expect, keeping these outbreaks under very close observation and management."
Following the press conference, Dr Graham Brown, consultant in communicable disease control for Public Health Wales, said more than 1,000 workers from Rowan Foods in Wrexham had so far been tested for the virus since Sunday.
He said: "This does not mean that the company has been identified as the source of the infection, or that finding additional cases means the infection is increasing.
"However, we are identifying previously asymptomatic individuals that work for Rowan Foods Ltd with the infection."
After confirmed cases at 2 Sisters rose to 200, Dr Brown said: "We have recorded an increase of 25 confirmed positive cases of coronavirus, bringing the total cases in the outbreak to 200.
"Since we commenced targeted testing last Thursday, over 400 members of staff have provided samples."
Darren Hughes, director of the Welsh NHS Confederation, said identifying the two outbreaks in North Wales provided "reassurance" that the country's track and protect system was working.
He said: "Over recent days we have seen localised outbreaks of coronavirus in Wales. This news is not unexpected and in some ways it provides reassurance that these cases have been found quickly and dealt with effectively.
"By finding these cases early, we can help to prevent transmission to the wider community. It is a testament to the track and protect system in Wales that we have been able to hopefully bring these outbreaks under control before more people were impacted."
Meanwhile on Tuesday, Public Health Wales said a further five people had died after testing positive for Covid-19, taking the total number of deaths to 1,483, while the total number of cases increased by 98 to 15,295.