It's not shifted. It's just there. It was never on the employees. Employees don't have their own money to tax. Employees money is employers money. That's its source.

Employees get taxed when they spend money by being consumers. Sales taxes and VAT are their tax burden. But income taxes of the employees are the burden of the employer. It's employer who has to fork that money because otherwise he wouldn't be able to pay enough so that the employee agrees to work.

The poster is referring to https://en.wikipedia.org/wiki/Tax_incidence