After the 2020 election, legal watchdogs, outraged at some of their colleagues, filed scores of ethics complaints against lawyers who used their skills in questionable ways to help former President Donald J. Trump stay in power.

And in the past few years, the groups have had some notable successes, securing judgments that have led to pro-Trump lawyers like John Eastman and Rudolph W. Giuliani having their law licenses deactivated.

Now, one of these groups — the 65 Project — is taking a more proactive approach. Starting on Thursday, the group’s organizers are planning to run advertisements in legal journals published in swing states, reminding lawyers that they are ethically barred from bringing false claims on behalf of any client.

“Don’t risk your law license by joining an effort to subvert democracy,” one of the ads says. “We — and the public — are watching.”

The ads, which are initially set to appear in both print and online in Arizona, Georgia, Michigan, Pennsylvania and Wisconsin, will be coming out just as Republicans and Democrats alike are gearing up for what could be an exceptionally bitter legal fight over the election.

Democrats are expecting an aggressive Republican effort to challenge voters, rules and, possibly, the results of the race. In preparation, Vice President Kamala Harris’s campaign has assembled an expansive legal team of hundreds of lawyers and thousands of volunteers meant to be a bulwark against multiple certification battles and mass voter challenges.