comma before 'that' [relative pronoun]: a petition, filed by..., that

The Law Society previously rejected a petition on Jan 5, filed by 44 lawyers, that had called for an extraordinary meeting to revoke the new travel policy.

Is the comma after 'lawyers' correctly used with the following word 'that'?

Thanks.

This is a good one!
'that' is correctly used...and so is the comma.
There's always some exception to a rule, even the 'comma,which' and 'no comma/that' rule for which I am a stickler; and here, by the interpolation of the "...by..."phrase
Thanks for that one Karen.

There must be a comma after "lawyers". That is not a relative pronoun of lawyers, which it follows, but of petition. "Filed by 44 lawyers" is a non-restrictive parenthetical phrase and can be omitted without affecting the meaning or grammatical correctness of the sentence.

If the sentence were as follows:
"The Law Society previously rejected a petition that had called for an extraordinary meeting to revoke the new travel policy."
a comma after petition would be wrong, as the following clause is restrictive of petition.

I agree that the comma following "lawyers" is correct. But the word following it should have been which, rather than "that", since the clause refers specifically to the previously mentioned petition.