Minn. Stat. § 357.22: WITNESSES.

The fees to be paid to witnesses shall be as follows:

(1) for attending in any action or proceeding in any court or before any officer, person, or board authorized to take the examination of witnesses, $20 for each day;

(2) for travel to and from the place of attendance, to be estimated from the witness's residence, if within the state, or from the boundary line of the state where the witness crossed it, if without the state, 28 cents per mile.

No person is obliged to attend as a witness in any civil case unless one day's attendance and travel fees are paid or tendered the witness in advance.