The RNLI's fundraising and communications director, David Brann, confirmed that Dialogue Direct called him around three weeks ago to terminate the contract.
Dialogue Direct's PR manager, Paula Morison, refused to comment on the move.
The RNLI was one of 62 charities "named and shamed" by the Campaign Against Arms Trade three months ago as owning shares in companies that export weapons. According to CAAT's Clean Investment Campaign report, the RNLI owns more than 360,000 shares in Rolls-Royce, almost 126,000 in GKN, and 27,670 in Cobham.
The RNLI had been using Dialogue Direct to carry out street fundraising for just under a year, Brann confirmed.
He said: "The agency told us they were no longer able to fulfil their contractual agreement with us. They said that if they were not able to recruit for us and do their job in a wholehearted way, it was best that we parted."
Brann said the RNLI had made no changes to its investment portfolio in the wake of the CAAT report because the investments it held were all legal and its trustees were bound to follow Charity Commission guidance to maximise returns. The guidance states that charities can only exclude certain shareholdings if they have a direct impact on the charity's objects - in the RNLI's case, to save lives at sea.
Brann accepted that if a particular investment adversely affected the charity's ability to raise funds, this would have a detrimental effect on its ability to save lives at sea. But he pointed out that street fundraising generates "only a tiny proportion" of the RNLI's income - so little, in fact, that the charity has not yet decided whether to appoint another agency.
"We are reviewing whether to continue with street fundraising," said Brann. "We fundraise face to face in lots of other ways, using volunteers and our own staff, in lots of situations such as at boat shows, which are much more effective than on the street."
Brann added that a lot of the charity's supporters were hostile to the technique.