Yes. Rule 1.5(e) of the Rules of Professional Conduct provides as follows:
A division of a fee between lawyers who are not in the same firm may be made only if
(1) the division is in proportion to the services performed by each lawyer or each lawyer assumes joint responsibility for the representation;
(2) the client agrees to the arrangement, including the share each lawyer will receive, and the agreement is confirmed in writing; and
(3) the total fee is reasonable.
Dividing Fees Pro Rata
If the lawyers will be dividing fees “in proportion to the services performed by each lawyer,” then here is an example of a provision to put into the agreement with the client:
Attorney fees will be divided between [firm 1] and [firm 2] in proportion to the services performed by lawyers in each firm.
You might was to clarify how “in proportion” will be calculated. For example, will the attorneys track their time and divide the proceeds by the hours expended? More often, attorneys track their time along with their usual billable rates (e.g. “value”), and the proceeds are divided to reflect the “value” contributed by each attorney/firm.
Dividing Fees Other Ways
In cases where the firms will not divide fees in proportion to the services performed by each lawyer (e.g. 33% to the referring attorney), here is a sample provision to put into your agreement with the client:
Attorney fees will be divided as follows: [firm 1] will receive two-thirds and [firm 2] will receive one-third. The attorneys assume joint responsibility for the representation.
When using this approach, note that the express language essentially will pierce the corporate veil of the law firms, making attorneys on the case personally liable for the acts of other attorneys on the case.