Different languages have different rules about how to use commas. You cannot use the punctuation rules of your native language when you write in English – you must use English rules.
Putting a comma before “that” is a very common mistake:
The claimant’s attorney stated, that his client was unable to attend the hearing.
The claimant’s attorney stated that his client was unable to attend the hearing.
In this example “that his client was unable to attend the hearing” is a subordinate clause. Languages such as German, Czech and Polish have the rule that a comma should be inserted before every subordinate clause. In English we do not have this rule (if we did, I would have put a comma between “rule” and “that” in the previous sentence).
This issue is not limited to subordinate clauses beginning with “that”. Here are some other examples:
Please review the draft to see, if it fully reflects your intentions regarding employee remuneration.
A VAT obligation arises, when the goods have been delivered.
The company should check, whether the contractor has the required experience.
Please review the draft to see if it fully reflects your intentions regarding employee remuneration.
A VAT obligation arises when the goods have been delivered.
The company should check whether the contractor has the required experience.
This sort of mistake matters in English because it can be very confusing for the reader. In English commas are used to mark places where the reader naturally pauses, or they are used to “section off” parts of sentences.
There is no natural pause before the subordinate clauses shown above, and there is no reason to section off the subordinate clauses from the rest of the sentences. Therefore such commas are incorrect.
Also – native English speakers never put commas in such places, so by doing so you’ll be giving a clear indication that English is not your first language.