As in previous year or like previous year.

He did not make any contribution last year. So we are not going to invite him for that this year.

As in previous year, we assume that you are not making any contribution to the society so that we are not seeking your contribution this year.

Like previous year, we assume that you are not making any contribution to the society so that we are not seeking your contribution this year.

Which one is more professional?

As in previous years / As in the previous year