Normally when I received an invoice from a counsaltant the procedures is that the company who pays the bill pays also the tax for the counsaltat. To better explain here below I put an example:

Invoice amount: 2000$

VAT: 21% = 420$

Total invoice: 2420$

Tax deduction: 20%= 484$

My company pays to the counsaltant: 2420-484= 1936$

My company pays to the tax agency as a third party payer: 484$

As per our procedure my company doesn't pay to the counsaltant the total amount, but only the 80%. Then my company has to pay the 20% to the tax agency. 

It's sth similar with the employers: The company pays to the employers just the net salary and pays for the employers the tax.

Hope I've been clear.

Thanks