The Left complains about the special exemption given to gun makers from liability lawsuits. But in fact, no manufacturer of anything should ever be held liable for the illegal use of their product.
Similarly in this case, the presence or absence of any infectious disease (unless it's a medical facility) is outside the purview of any employer and so outside their liability and only the government should be able to issue mandates like this with explicit limitations even on that power.
It's more complicated than that.
For one thing, you'd need a constitutional amendment to completely change the way Federal and state courts work. Torts are covered by state law, not Federal law -- unless the issue at hand involves a Federal party or an issue covered by Federal law. What you're proposing would completely revolutionize the way civil lawsuits are adjudicated in the future.