It should have been simple: one Filet-O-Fish meal, hold the cheese.

But McDonald's regular Melanie Michels was "baffled" this week when staff at an Auckland restaurant insisted her burger couldn't be altered because it was part of a WeightWatchers-approved package.

Michels, 22, said the manager of the Grey Lynn branch on Great North Rd backed up the decision, even when told she was allergic to cheese.

"It baffled me.

"I can understand that it's a WeightWatchers-approved meal, but I wasn't adding cheese, I was taking away the fattiest part of the burger."

Refusing the special order meant Michels couldn't eat the meal, and left the restaurant empty-handed.

She could have ordered the same three items - a burger, salad and diet drink - individually, with cheese removed from the burger, but that would have cost $11.50, rather than the meal price of $8.70.

When Michels complained by email to McDonald's New Zealand head office, their reply confirmed the policy: "We understand your frustration at not being able to remove the cheese ... and we agree that at the outset, this does seem such a small change.

"However, any additions or deletions change the overall points value of the meal and the meal is no longer a WeightWatchers-Approved meal."

But Michels said she'd bought the meal without cheese several times previously.

And when the Herald on Sunday visited the same restaurant the day after, the no-cheese order was taken without question.

McDonald's launched three WeightWatchers-approved meals on March 3 with an extensive advertising campaign, and said there were plans for further options for slimmers.

The plan involves eating food worth a set number of "points" every day.

McDonald's spokeswoman Kate Porter said they couldn't sell the Filet-O-Fish meal with variations because it would change the advertised "points" value.

Porter said removing cheese would "obviously make it lower in calories", but a blanket no-changes policy was easier for staff to manage.

"We understand this may seem frustrating, and to date we have received about five similar queries from customers," she said.

"We have taken the customer's feedback on board and will be looking to see whether we can make deletions easier."