Colonel Bob Stewart has said that allowing Chinese company Huawei to bid for contracts for the new 5G network could make the UK “vulnerable to cyber-attack”.
Gavin Williamson was sacked as defence secretary after he was accused of leaking details about Huawei’s possible involvement in 5G from a National Security Council meeting.
Mr Williamson has denied leaking the information.
But Mr Stewart, the Conservative MP for Beckenham, told talkRADIO’s James Whale the security services have "strongly advised" that Huawei should not be involved.
“Apparently the security services have strongly advised that Huawei should not be involved in our 5G network," he said.
“If that is the case, I would take that advice very seriously. Apparently the Prime Minister has not taken that advice very seriously.”
The Conservative MP added: “We are rendering ourselves vulnerable to a Chinese cyber-attack and infiltration into our most sensitive systems. I don’t understand why the decision has been made.”
A Downing Street spokesman said on Wednesday that the prime minister had "lost confidence" in Mr Williamson's ability to serve as defence secretary.
In a letter from Theresa May to Mr Williamson, she wrote that there was no other "credible version of events" that explained the leak.