The Tories' "imposition" of a general election candidate in Bridgend could cost the party one of its main target seats, a regional official has warned.
Karen Robson was confirmed as Conservative candidate for the constituency on Tuesday evening.
South West Wales Tory chairman Alex Williams said Bridgend members felt "aggrieved" that a local candidate had not been added to the shortlist.
Labour MP Madeleine Moon will defend a 1,927 majority over the Tories in June.
Ms Robson said: "I am honoured to have been selected to be the Conservative Party candidate for Bridgend."
Mr Williams and another party figure told BBC Wales that Conservative Party headquarters initially shortlisted Ms Robson, who has previously stood for Westminster and assembly seats in Cardiff, and Dan Boucher, a regional Tory candidate for South Wales West in the 2016 assembly poll.
This prompted the Bridgend branch to ask for a "local" candidate to be added to the shortlist, but party headquarters then decided to select Ms Robson without a branch vote.
Mr Williams, who is also on the board of the Welsh Conservatives, said: "I'm personally very disappointed, it's highly undemocratic and has caused significant problems.
"Many members are aggrieved and many are thinking of leaving the party as a result.
"It appears the motive is to ensure more Welsh Conservative female MPs.
"We mustn't ensure gender balance in the parliamentary party by enforcing female candidates on local branches.
"This has given Labour ammunition to say the Conservatives don't have a local candidate - the decision could cost us the seat."
'Angry and disillusioned'
Ken Watts, the only Conservative on Bridgend council, said he was "angry and disillusioned" members were not given a chance to select a "local" member.
He believes members should have been able to select Mr Williams, who is also the agent for Tory candidates standing in Bridgend in Thursday's local election.
"I will find it extremely difficult to campaign for her," he said of Ms Robson.
"It's a point of principle - nothing personal.
"It's been a four-year struggle to get Bridgend as a target seat and we've finally achieved that. Alex fought really hard to help make that happen.
"I'm very disappointed in the approach from CCHQ [Conservative Campaign Headquarters] - I'm angry and disillusioned, some senior members feel it could cost us the seat."
Plaid Cymru has selected Rhys Watkins as its candidate for Bridgend.
BBC Wales understands a Conservative candidate was also imposed in Newport West, where Angela Jones-Evans has been selected, despite local activists wanting to have a choice.
Sources in the city said that there had been only one candidate available for the Newport West conservative association to choose from.
Activists told the BBC that they liked Mrs Jones-Evans as a candidate, but believed it would have helped her if members could have voted for her from a shortlist of more than one.
There had been hopes the party would change its mind, but at a selection meeting on Sunday only one candidate was put forward.
There was known to be some limited opposition to the imposition of a candidate at the meeting, but the association in the end endorsed Mrs Jones-Evans.
Nick Webb, a local Tory activist and the candidate for Newport West in 2015, was understood to have wanted to have run and is known to have been upset that his proposed candidacy was not put to a vote of activists.
The Plaid Cymru candidate in Newport West is Lewis Greenaway.
Labour MP Paul Flynn will be defending a Labour majority in Newport West of 3,510 over the Conservatives.
A full list of candidates will be available following the close of nominations on 11 May.