Political parties at Westminster must take steps to ensure the upcoming review of constituency boundaries does not result in a reduction in the proportion of women in parliament, says a cross-party committee of MPs.

The Women and Equalities Commission is launching an inquiry aimed at ensuring the redrawing of Britain’s political map, which will cut the current 650 constituencies to 600, doesn’t disadvantage women.

The changes will pit existing MPs against each other, where two adjacent seats are merged to become one, or three become two. Maria Miller, the committee’s Conservative chair, said female MPs could find themselves disadvantaged in this process if parties do not take active steps to protect female representation.

“There will be such a significant reduction in the number of seats that we believe parties need to think about this carefully, particularly given the progress that was made at the last election in increasing the number of women in parliament,” she warned.

“The threats are clear: that many of the women who are in parliament are more likely to be in marginal seats; they tend to have shorter tenure; and the evidence from workplaces in general suggests they tend to be not as successful at negotiating.”

The Boundary Commission, which is redrawing constituencies, will publish its initial findings next month, and the parties will then have the chance to appeal. Of the 650 seats currently in the House of Commons, men hold 458 (70%) and women 192 (30%).

Miller and her colleagues, who include Labour MPs Jess Phillips and Ruth Cadbury, will take evidence from experts, and plan to publish their findings within weeks, to feed into parties’ thinking about how to respond to the Boundary Commission’s initial report.

One potential proposal could be for female MPs to be given priority over their male colleagues, where seats are being merged, to ensure that the proportion of women in parliament does not fall, for example.

The committee will also examine recent proposals from the Good Parliament report, which called for working practices in the House of Commons to be made more family-friendly to encourage more parents to take on the job of being an MP.

Theresa May played a key role in boosting the number of Conservative women in parliament as a co-founder of Women2Win, a group that aimed to get more women selected for winnable Tory seats.

Miller said: “In my party, I don’t just want to see Theresa May as prime minister with more women on the frontbench, but even more female representation on our backbenches too.”

The new constituencies – which are expected to advantage the Conservatives by reflecting the shrinking population of some former Labour strongholds in the north, are due to be in place in time for a general election in 2020.

Some Labour MPs fear that if Jeremy Corbyn sees off the leadership challenge from Owen Smith, he could take the opportunity of the boundary reforms to unseat his parliamentary critics.

Compulsory re-selection for MPs was a key tenet of the Campaign for Labour Party Democracy, of which Corbyn was a founder member; but Labour’s chief whip, Rosie Winterton, has insisted she remains in charge of the process of how Labour will decide which sitting MPs will contest the new seats.