Ontario MP Bruce Hyer quit the NDP caucus today, saying he can better represent his constituents as an Independent MP.

The MP for Thunder Bay–Superior North explained his decision in a statement and in an interview with CBC News. He said the way political parties impose control on the way their members vote is at the heart of his decision. He referenced the votes on the long-gun registry and how the party required members to support the registry as an example, and said he refuses to be told how to vote.

"All three main parties have for a long time been requiring lockstep discipline and there’s little room for any kind of meaningful public debate and for putting constituents ahead of party politics," he said.

Hyer said he is not giving up his NDP membership and says he'll vote with the party most of the time, but that NDP Leader Tom Mulcair's promise to bring back the long-gun registry if his party wins the next election and his intention to direct any votes on it, was also behind his decision.

He noted that supporting the controversial long-gun registry is the party's current position but it is not in the NDP platform, meaning it is not official party policy and that is another reason that votes on it should not be directed.

Hyer recently contradicted his party's position on the long-gun registry when he sided with the Conservatives in the final vote to end the registry in February.

The NDP's interim leader at the time, Nycole Turmel, had already disciplined Hyer for voting with the government during a previous vote in the fall. Another northern Ontario MP who voted with the government, John Rafferty, was also disciplined.

They were punished by not being allowed to ask questions in the Commons chamber and were stripped of critic responsibilities.

Hyer had always opposed the registry and consistently voted with the Conservatives to abolish the requirement to register long guns.

Hyer excluded from shadow cabinet

He said in his statement that the gun registry is an example of how parties can't compromise.

"Mr. Mulcair has made it clear he will bring back the long gun registry, and will use the whip. I am also concerned that Mr. Mulcair does not seem willing to cooperate with other parties on important issues. And on climate change, parties are hopelessly locked to cap and trade or outright inaction, making compromise to achieve even piecemeal progress impossible," he said.

Hyer went on to note that he was left out of Mulcair's new shadow cabinet. Mulcair, who was elected leader last month, named 54 MPs to critic portfolios and another 23 were given deputy critic roles.

"One of the jobs of any new leader is to unite their party, and there are different ways to do that. Being excluded from any position was a clear message that my constituents will be muzzled," Hyer said.

Mulcair said he found out about Hyer's decision right before question period. He said it is not an ideal situation but that Hyer had made it clear to him that he felt he should not be bound by party lines.

"Bruce simply feels that he's allowed to come up with his own decisions," Mulcair told reporters.

The NDP leader said he couldn't name someone to the shadow cabinet who is not willing to follow the party's policy decisions.

"Bruce is not able to work within that system, the result is his departure today," Mulcair said. He also said he had lifted the punishments on Hyer and Rafferty in an effort to show they had "turned the page."

Hyer is now the second MP to leave the NDP caucus since last May's election that saw the party win Official Opposition. Lise St-Denis, a rookie MP from Quebec, jumped to the Liberals in January.

Hyer was first elected as a New Democrat MP in 2008, after running twice unsuccessfully.

Members of Parliament were back in Ottawa after a two-week break in their ridings and earlier in the day, NDP House leader Nathan Cullen said his 102-member caucus was returning united and focused on holding the Conservatives to account.