Advocates for worker safety say the workplaces of over a million Canadians are about to become more dangerous because of proposed changes to the Canada Labour Code.

One person who is concerned is Rob Ellis, whose teenage son David was drawn into an industrial mixer at a bakery in Oakville, Ont., in 1999.

David hung on for six days in hospital before he died.

Since then, Ellis has been teaching youth and employers how to make work safer through his not-for-profit foundation, My Safe Work.

"It was the second day on the job for our 18-year-old son and he lost his life," said Ellis at a news conference on Parliament Hill Wednesday. "I'm really concerned that if Bill C-4 gets passed that David's story will be more common."

The federal government is proposing changes to the Canada Labour Code as part of its omnibus budget bill, C-4. The code covers about 1.5 million federal employees in sectors such as railways, shipping, pipelines and mining. Two areas of concern

The proposed legislation would change health and safety laws that govern the right of workers to refuse unsafe work.

Safety advocates and labour groups are particularly concerned with two changes.

One of the changes would give the minister of labour the power to determine, without investigation, whether a refusal to work is trivial, frivolous or vexatious. That finding could mean an employee is disciplined, including being fired.

"So who's going to stick up their hand in those circumstances?" asks Bob Kingston, president of the Agriculture Union, which is part of the Public Service Alliance of Canada. Under current legislation, if an employee and employer disagree on whether something is safe or not, an investigation by a health and safety officer is a must.

Another area of concern is that the definition of danger would change from the broad idea of potential hazard to something that poses an imminent or serious threat.

Kingston said by narrowing the definition of danger it will make it harder to prove work is unsafe.

"If this goes through, it's going to kill people. It's as simple as that," Kingston said, adding the proposed changes were devised without any consultation with health and safety experts or labour representatives. 18-month fight

Maureen Harper, a retired veterinarian who worked with the Canadian Food Inspection Agency heading up its BSE (mad cow) program, fought for almost 18 months to prove the air in her building in Mississauga, Ont., was making her and others sick.

Burning eyes, respiratory difficulties, dramatic temperature swings and the smell of sewer gas were just some of the complaints.

Eventually, tests showed a number of problems, including a high count of Legionella bacteria on the roof's cooling stack, that was located near an air intake vent.

With a threat of Legionnaire's disease, the building was shut down for a month and fixed.

"Management was in denial from my point of view, and the clinical symptoms were subtle and non-specific, so hard to prove that there's a problem with the building and that is causing compromised health for the people working there," Harper said in an interview with CBC News.

"Through the course of people issuing work refusals, we discovered there were a lot more things going on in the building than we ever dreamed of from the beginning," Harper said.

She said it was an uphill battle and the proposed changes would likely make it even harder to get an investigation or prove their case. Minister defends changes

In fact, she said she would think twice about coming forward under the proposed legislation for fear of being fired without even an investigation.

But Minister of Labour Kellie Leitch said the changes will actually make workplaces safer.

In an interview with CBC News, Leitch said health and safety of workers is her number one concern.

"This is something extremely important to me. I'm a pediatric orthopedic surgeon. I want to make sure every Canadian citizen goes home with all their fingers and toes. They have to go home safely to their families. Those that they left in the morning," she said.

She said between 2000 and 2010, eighty per cent of refusals to work were found to be situations of no danger.

"These requests put a huge strain on resources. And it means our health and safety officers...can't concentrate on the areas where they really should be."

Leitch argued a clearer definition of danger will help free up those officers to do more proactive interventions.

Bob Kingston refutes that 80 per cent number, arguing that many times when a health and safety officer goes to a workplace, he or she is able to help find a solution to the danger on the spot, avoiding a major work stoppage. He said that translates into a finding of no danger, even though technically there was one.

Rob Ellis points to the government's own numbers that show a 22 per cent decline in the rate of disabling injuries between 2007 and 2011 as proof the current system is working and does not need to be changed.