Humberside Police may have to lose 132 officers to fund increased contributions to the Police Pension Scheme, the chief constable has warned.
Lee Freeman said proposed government plans would cost the force £2.6m in 2019/20, rising to £6.6m from 2020/21 onwards.
He said cutting officer jobs would be a "significant setback" in efforts to reduce crime and protect communities.
The Home Office said it was working closely with police on the issue.
A cross-party group of MPs is now seeking talks with Home Secretary Sajid Javid.
They have written a letter to him asking him to meet to discuss the matter.
Humberside Police said if the changes went ahead without additional funding, it would have to lose 52 officers in 2019/20 and 80 in 2020/21.
This would take officer numbers down to that of the 1970s, according to the chief constable.
He said he would have to consider whether he could retain Police Community Support Officers (PCSOs) with such a reduced budget.
The letter has been signed by Diana Johnson, Labour MP for Hull North; Emma Hardy, Labour MP for Hull West and Hessle; Andrew Percy, Conservative MP for Brigg and Goole; Sir Greg Knight, Conservative MP for East Yorkshire; Martin Vickers, Conservative MP for Cleethorpes; Melanie Onn, Labour MP for Great Grimsby; Karl Turner, Labour MP for Hull East; and Nic Dakin, Labour MP for Scunthorpe.
It reads: "With recent reports about violent attacks on Humberside Police officers, it is clear to us that our local police need to be supported."
The Home Office said: "We are working closely with forces to understand the impact this change will have and are in discussions with police leaders about mitigating the impact on the front line.
"The government is committed to continuing to ensure that the police have the resources they need to do their vital work and the Home Secretary has been clear that he will prioritise police funding."