Federal minister Simon Birmingham has blamed personal attacks by "green and left activists" for South Australian MP Nicolle Flint's decision not to recontest her seat.
The two-term Liberal member announced on Friday she will not run in the next election, but has not publicly explained the reasons for her decision.
Mr Birmingham said Ms Flint's office was vandalised during the last election, and she had been harassed online by left-wing groups including GetUp and Extinction Rebellion.
"She faced a very bitter election campaign last time, that saw appalling behaviour against her," he told reporters on Saturday.
"Those people ought to take a good long hard look at themselves," he said.
Ms Flint has been vocal about problems facing women MPs, calling out what she described as sexist "rubbish" they have been forced to deal with.
But Mr Birmingham defended the level of support the Liberal party had provided for Ms Flint, saying party leaders had discussed the best way to back her in a challenging environment.
He said he and the prime minister had "continued to engage" with Ms Flint in the expectation she would run for the Liberals in the next election.
Mr Birmingham did not directly answer questions about whether low numbers of women in the Liberal party may have contributed to Ms Flint's choice.
Prime Minister Scott Morrison issued a statement on Friday night, also taking aim at "unacceptable behaviour".
"The public attention from being a parliamentarian does sometimes attract unacceptable behaviour, and I have admired Nicolle's efforts to stand against the bullying and nastiness of particular groups and individuals," Mr Morrison said.
"I wish her all the best for what comes next."
In a statement issued on Friday Ms Flint promised to continue working for her electorate until the election.
"It has been an honour to represent the people of Boothby over two terms and I am grateful to them, and to my Liberal Party members, for giving me this opportunity," Ms Flint said in a statement.
Ms Flint's Boothby electorate is held by a margin of 1.4 per cent.
Australian Associated Press