Can a lawyer take a case against a former one-time client in a totally unrelated matter that does not involve the former client's confidences?
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This page answers the general question as of 1981. Ezel answers yours: whether it's allowed on your facts, under the current Illinois Rules of Professional Conduct, with citations.
Plain-English summary
A lawyer had represented a general contractor as plaintiff in a suit on a public construction contract, which settled on terms not fully satisfactory to that client. Within a year, the same contractor brought a different suit, on a different construction contract, against parties who retained that former lawyer; the lawyer asserted the same types of defenses he had raised in the first suit. The question was whether a conflict disqualified the lawyer from the second suit.
The committee answered on two assumptions: that the lawyer was not engaged as the contractor's general attorney during the contract and performance underlying the second suit, and that the facts of the second suit were completely unrelated to the first. On those assumptions, it found no conflict under Canon 5 and Rule 5-105. Employment to handle an isolated, ad hoc matter does not, after completion, absolutely foreclose later employment for another client adverse to the first (citing Opinions 603, 581, 569 and ABA Informal Opinion 1233).
The committee added that the assumptions ruled out the Canon 4 confidentiality prohibitions: Rules 4-101(b)(2) and (3) bar a lawyer from using a client's confidence or secret to the client's disadvantage, or for the advantage of the lawyer or a third person, absent consent. It concluded that the lawyer's advocating opposite viewpoints on the same or similar issues does not, by itself, create a conflict under Canon 5.
Currency note
This opinion was issued in 1981, under the former Illinois Code of Professional Responsibility and before Illinois adopted the 2010 Rules of Professional Conduct. The ISBA Board of Governors affirmed the opinion in July 2010 as generally consistent with the 2010 Rules (Rules 1.6(a) and 1.9), while cautioning that the specific standards referenced may differ from the 2010 Rules. Subsequent rule amendments or later opinions may have changed the analysis. Treat this page as historical context, not current guidance. Verify against current rules before relying on any specific rule or requirement mentioned here.
Common questions
Q: Can a lawyer take a case against a former one-time client?
A: The opinion concluded it is not per se a conflict, where the new matter is totally unrelated to the prior representation and does not involve the former client's confidences or secrets.
Q: Does it matter that the lawyer is now arguing the opposite side of similar issues?
A: Per the opinion, advocating opposite viewpoints on the same or similar issues does not, by itself, create a conflict of interest under Canon 5.
Q: What would change the answer?
A: The committee's conclusion rested on assumptions that the lawyer was not the client's general attorney and that the matters were unrelated; using the former client's confidences or secrets would implicate the Canon 4 prohibitions.
Background and rules framework
The opinion applied Illinois Code of Professional Responsibility Canon 5 and Rule 5-105 (conflicts), and Canon 4 with Rules 4-101(b)(2) and (3) (use of a client's confidences and secrets). The Board's 2010 affirmation maps the analysis to current Illinois Rules of Professional Conduct 1.6(a) (confidentiality) and 1.9 (duties to former clients), corresponding to ABA Model Rules 1.6 and 1.9.
Citations and references
Rules of Professional Conduct:
- Illinois Code Canon 4; Rules 4-101(b)(2), (3); Canon 5; Rule 5-105 (applied in the opinion)
- Illinois RPC 1.6(a), 1.9 (2010 equivalents per the Board's affirmation)
- MR 1.9 (duties to former clients); MR 1.6 (confidentiality)
Other opinions cited:
- ISBA Opinions 603, 581, 569: ad hoc representation does not foreclose later adverse employment
- ABA Informal Opinion 1233: representation adverse to a former client in an unrelated matter
See also
- ISBA Ethics Op. 724: Opposing the Client of a Lawyer You Represented
- ISBA Ethics Op. 790: Representing a Party Against a Former Client
- ISBA Ethics Op. 05-01: New Client in a Matter Involving a Former Client
Source
- Landing page: https://www.isba.org/ethics/opinions/753
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