Montgomery County officials are challenging a petition that could lead to the repeal of a recently enacted law that scales back the collective bargaining rights of the county police union, according to a county official.

In a memo issued last week, County Attorney Marc Hansen said the county has hired a local election law specialist, Jonathan S. Shurberg, to challenge the petition.

County election officials concluded this month that the petition, which was circulated by the Fraternal Order of Police Lodge 35 police union, drew enough signatures for a referendum next year on the law.

Passed unanimously by county legislators, the law took aim at “effects bargaining,” a process that allows the union to negotiate with county officials not only on wages and benefits but also over day-to-day duties, such as regularly checking e-mail.

When the bill was introduced, it struck a nerve with the police force. A packed public hearing on the bill in July had some officials pleading for understanding while others shouting in frustration. Many police officers walked out during the hearing.

Shortly after the bill was passed in July, the union started work on the referendum petition. The union hired a petition-gathering firm and worked with members and volunteers to collect signatures, union officials said.