PORTLAND – A national environmental group urged the boycott of Royal Caribbean Cruises on Thursday.

Oceana says the leading cruise-ship line dumps partially treated wastewater into the ocean. It asked potential travelers to sign pledges saying they won’t do business with the company until they install equipment that completely treats sewage.

The group kicked off the campaign in Portland the same day the Royal Caribbean ship Grandeur of the Seas made a daylong visit.

An Oceana spokesman said the group’s goal is cleaner operations throughout the cruise industry, and that Royal Caribbean is the start.

“They have touted themselves as an environmental leader in the industry,” said Sam Haswell of Oceana. In 1998 and 1999, the company paid more than $26 million “for illegal discharges of oil, wastewater and garbage and for falsifying records,” he said.

Three of the company’s 26 ships have equipment to treat sewage completely before discharging it, he said. The rest of the ships have partial treatment systems, which are legal under an exemption in the Clean Water Act, he said.

“They’re one of the biggest cruise companies out there and we think they can be a great example for the industry,” Haswell said.

Royal Caribbean issued a brief statement Thursday in response to the campaign.

“We believe Oceana has seriously misrepresented Royal Caribbean’s environmental practices,” it said. “We have met with representatives of the group and tried to educate them about our policies and procedures but have been frustrated by these discussions. We would like to resolve our differences and look forward to future opportunities to discuss these issues.”

Material posted on the company’s Web site says Royal Caribbean ships follow procedures that exceed legal standards. Partially treated sewage is discharged when ships are 12 or more miles from shore and moving at 6 knots or faster, even though there are no such requirements, according to the company.