New Democrats are not just holding a policy convention this weekend — they're throwing themselves a birthday party.

The three-day gathering in Vancouver will feature a celebration to mark the NDP's 50th anniversary, and now that its 103 MPs form the Official Opposition, members say they have plenty of reasons to party.

"We're going to be celebrating our past achievements," said Kathleen Monk, NDP Leader Jack Layton's director of communications. "And looking at our more recent gains, becoming the official opposition, and looking to our future."

The policy convention gets underway Friday, and the strike by Air Canada workers has forced some MPs and other delegates to change their travel plans so that they don't cross picket lines. It's a NDP policy to use companies and services whose workers are unionized, where possible. Taking the train or driving aren't viable alternatives for MPs heading west from Ottawa because of their tight timetables and some are flying WestJet as a result.

Aside from the anniversary festivities, more than 1,500 delegates are expected to participate in a number of policy debates that will shape the party's future.

Constitution change up for debate

One of the resolutions that will be up for discussion gets at the very heart of the NDP: a proposal to change its constitution.

At the last policy convention in Halifax in 2009, members voted in favour of changing the preamble of the party's constitution and the new wording will be voted upon this weekend.

Brad Lavigne, the party's national director, said the idea is to modernize its language because terms used in the existing constitution are outdated.

"This is just about using inclusive language that is in keeping with terms that are expressed in the 21st century," said Lavigne, who on Wednesday was appointed to a new job as Layton's principal secretary.

The current preamble reads: "The New Democratic Party believes that the social, economic and political progress of Canada can be assured only by the application of socialist principles to government and the administration of public affairs."

It goes on to outline the principles of democratic socialism and says the NDP is "proud to be associated with the democratic socialist parties of the world and to share the struggle for peace, international cooperation and the abolition of poverty."

The proposed new preamble instead says that the New Democratic Party believes that "social justice, equality, and environmental sustainability are vital to achieving a strong, united and prosperous Canada for all."

It also says the NDP is "the voice of working people" in Parliament, advocating for their interests, and that New Democrats are "proud to stand in solidarity with its allies around the world working for international peace and justice, ending discrimination and exploitation, eliminating poverty and that wealth and power are in the hands of many and not the few."

Lavigne said changing the wording is simply about adding more contemporary language that is used by everyday Canadians.

No merger with the Liberals

Another policy resolution that stands out is a call for the NDP to reject any proposals to merge with the Liberal Party. It also says that the NDP should "extend a warm welcome to all former Liberal supporters who wish to join the genuine anti-Conservative opposition — the NDP."

In the wake of the May 2 election that saw the Liberals decimated to 34 seats, there were musings about a Liberal-NDP merger to oppose the Conservatives. Some Liberals, including the party's interim leader Bob Rae, have said that talks about that idea are inevitable as the party rebuilds. Rae did not advocate for a merger, but said people will talk about one.

The merger rejection resolution comes from the NDP's Toronto Centre riding association, the riding that is represented by Rae.

When speaking about the resolution, Lavigne said the NDP is feeling a great sense of optimism about the party's future.

"We'll wait to see how delegates respond but there's a tremendous amount of enthusiasm," he said. "The results of May 2 offer, I think, some food for thought on the future of the party."

Other policy resolution topics include health care, the environment, pensions and employment insurance, and education.

Layton said New Democrats will be more concerned about those issues than about the wording of the constitution's preamble.

"These are the issues that have driven our party for so many years and we are going to stay focused very much on those," he said Wednesday.

Layton, who moved into the opposition leader's official residence on Wednesday, said he's looking forward to the policy discussions.

"There are many proposals in front of our convention," he said. "There will be an enthusiastic discussion about all of those. We've been a party for 50 years and so the idea that there be discussion about our goals and objectives, I think is good."

The party's birthday party will be held on Friday night, and on Saturday after a day full of policy discussions, there will be a "Next Generation Showcase" that will focus on some of the NDP caucus' younger MPs. Newly-elected Rathika Sitsabaiesan, 29, will be among the rookie MPs to deliver a speech.

Nova Scotia's NDP Premier Darrell Dexter is attending the convention and will speak Saturday. The convention will also hear from campaign strategists who will talk about what they view as keys to the NDP's success on May 2.

On the final day of the convention, Layton will make his address. Just ahead of his remarks, delegates will be asked whether his leadership should be reviewed. If they vote in favour of a leadership review, the party would then undertake to organize a leadership race within 12 months.