B-1, r. 3.1 - Code of Professional Conduct of Lawyers

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123. A lawyer must not, directly or indirectly, pay or offer to pay compensation to a witness or offer the witness any other benefit which is conditional upon the content of his testimony or the outcome of the matter.
However, a lawyer may agree to pay:
(1)  reasonable expenses incurred by a witness to appear or testify;
(2)  reasonable compensation to a witness for loss of time in appearing or testifying; or
(3)  reasonable fees for the professional services of an expert witness.
O.C. 129-2015, s. 123.