WASHINGTON (AP) — Republicans in the House want to hold up new federal rules intended to crack down on ivory sales because it is becoming more difficult for owners of musical instruments, antiques and guns made with ivory to trade in such items.

A House Appropriations subcommittee acted Wednesday to block the rules as part of a measure funding the Fish and Wildlife Service. The legislation has a long way to go before it becomes law and the rules, announced in February, will stay in effect in the meantime.

The rules are aimed at combating elephant and rhinoceros poaching at a time when illegal trade in ivory is flourishing. 

“It is extremely difficult to differentiate legally acquired ivory from ivory derived from elephant poaching,” senior Fish and Wildlife Service official Robert Dreher said in congressional testimony last month. “Our criminal investigations and anti-smuggling efforts have clearly shown that legal ivory trade can serve as a cover for illegal trade.”

Critics say the administration hasn’t made the case that shutting down trade in ivory items made from long-dead elephants discourages elephant poaching now or stops trade in illegal ivory.

The legislative effort is in in response to complaints that the rules are making it impossible in many cases for owners of objects made of ivory legally imported before bans imposed in 1975 and 1990 to sell such items, thereby undermining their value.

“The ban would make American owners of legal, pre-ban ivory potential criminals overnight, as well as strip their pieces of commercial value, adversely impacting the finances of millions of Americans,” a coalition of groups opposing the ban wrote the agency this spring.

Under the rules, interstate ivory sales are prohibited, except for “bona fide antiques” that are at least a century old. Sales of such ivory within a state are banned unless the seller can prove it was legally imported before the 1990 ban for African elephants or the 1975 ban on ivory from Asian elephants. In May, the government eased the rules somewhat for owners of musical instruments made with ivory.

Antique ivory has a variety of purposes. For instance, it’s often used for knife and handgun handles, as part of violin bows and parts of vintage guitars, antique chess sets and walking sticks.

Fish and Wildlife Service spokeswoman Claire Cassel said the agency had no comment.