The Trump campaign has been videotaping Philadelphia voters while they deposit their ballots in drop boxes, leading Pennsylvania’s attorney general to warn this week that the campaign’s actions fall outside of permitted poll watching practices and could amount to illegal voter intimidation.

The campaign made a formal complaint to city officials on Oct. 16, saying a campaign representative had surveilled voters depositing two or three ballots at drop boxes, instead of only their own. The campaign called the conduct “blatant violations of the Pennsylvania election code,” according to a letter from a lawyer representing the Trump campaign that was reviewed by The New York Times. The campaign included photos of three voters who it claimed were dropping off multiple ballots.

“This must be stopped,” a local lawyer for the Trump campaign, Linda A. Kerns, wrote in the letter, adding that the actions “undermine the integrity of the voting process.”